I was confused by the Defense rolls in One Roll Engine for a time, mostly because the rules are all separated into separate sections throughout the book. I'll try to clarify how to roll defense in most combat engagements.
Dodging[]
If you want to simply Dodge and do nothing else, you roll your Coordination + Dodge skill. If you roll one or more sets, you Dodge (although it may not be successful), and you must choose a single set from the roll. Each die in the single chosen set represents a Gobble die and removes dice directly from your opponents who are attacking you. For example, if you choose a set with a width of 3, you get 3 Gobble dice. You can distribute the Gobble dice against any number of attackers, but unless you take multiple actions to dodge, you can only choose one set from your roll.
If you reduce the attack to a width of 1 with Gobble dice, the attack misses. If an attack roll exceeds the highest width of your dodge set, you cannot apply the Dodge to that attack (the attack is too fast for you to dodge). If an attack roll is greater than (but NOT equal to) your height, you cannot apply the Dodge to that attack (the attack is too well-placed for you to dodge). Note that in the case of a tie, the Defender wins.
If you want to combine a Dodge with an Attack roll, you'd take the usual standard -1d penalty for multiple actions and roll with the smaller pool of dice. If you have multiple sets, you can use two sets, one for Attacking and one for Dodging.
You cannot Dodge for other people, but you can Dodge INTO an attack. In this case, instead of Gobbling attack dice, you use your dice to absorb an attack that is meant for another person. The rules for this aren't clear, but I'd guess that you would need a single set that equals or exceeds the incoming attack set in both height and width.
Limitations on Dodging[]
In order to dodge bullets or lasers or any effect that is around the speed of sound or faster, you need to have at least 6d in your Coordination stat or your Miracle dice pool. This group of fast attacks includes anyone with the "Speeding Bullet" extra attached to their Attacks Quality.
Alternatively, you need to have nearby cover to dive for. If the Attacks Quality has Penetration that can beat the armor rating of the cover, though, it is worthless.
You only get to use one set per roll with some exceptions. If you take a -1d to your pool for Multiple Actions, you can potentially Dodge twice (or -2d for Dodging three times, etc.). If you use a Defends Quality Miracle to dodge which has a Duration (or longer) Extra, you can use your chosen set for each and every attacker that goes against you.
Dodge as a Defends Quality[]
If you want to have a power that emulates hyper-speed and dodging, you would either have a Miracle (Superspeed, Shadow-blink, whatever) with a Defends Quality or a Dodge Hyperskill, possibly combined with a Coordination Hyperstat. Remember, Hyperskills can have one Quality, and the Dodge Hyperskill typically comes with the Defends Quality linked to it (not sure how you would use it any other way).
Hyperskills and Hyperstats can have Extras and Flaws, just like a Defends Quality. Depending on how you stat up your powers, though, having a Dodge Hyperskill is the cheapest way to do it (since Hyperskills are 1/2/4), followed by a Miracle with the Defends Quality (base 2/4/8 per die, with flaws reducing it to a minimum of 1/2/4), followed by the Coordination Hyperstat (base 4/8/16 per die). But obviously, the Coordination Hyperstat is more useful (applying to a number of skills), making it worth more anyway. Also, the Defends Quality on the Dodge Hyperskill typically cannot have a Duration/Endless/Permanent extra, at least not in the same way that a Miracle with a Defends Quality can have these extras (Up to GM approval, of course).
Some extras are more useful than others, when it comes to Defends. Duration/Endless/Permanent extras allow you to use your chosen set against every single attacker that attacks you individually (instead of just one set versus several rolls).
Adding the Interference (+3) Extra allows a Defends Quality to gobble dice BEFORE any other action takes place. It's like an uber-version of "Go First", making Width irrelevant. In fact, with the Armored Defense flaw, it makes that Defends Quality the equivalent of Heavy Armor (explained below), instead of a Dodge.
Blocking[]
If you want to simply Block and do nothing else, you roll your Body + Block skill. Otherwise, the rules are very similar to Dodging attacks. If you roll one or more sets, the Block is a success, and you can choose a single set from your Block roll to defend against attacks, with a number of Gobble dice equal to the width of the chosen set.
If you want to combine a Block with a Ranged Attack roll, you'd take the usual standard -1d penalty for multiple actions and roll with the smaller pool of dice. If you have multiple sets, you can use two sets, one for Attacking and one for Blocking.
Sounds a lot like Dodging, eh? Well, Blocking has special rules attached to it.
If you combine Blocking with a Melee Attack, you do NOT take the -1d penalty for multiple actions (woo!). You still roll the smaller pool of dice, and you have to use at least one set for Blocking. Additional attacks or blocks accrue the same amount dice penalties, however. On the plus side, you can feasibly combine a Melee Attack, a Block, AND a Dodge all in one roll, for only -1d.
If you block Shock damage, there are no ill effects. If you block Killing damage, either an arm or a parrying item takes a point of Killing damage. If you block Killing + Shock damage, your arm or a parrying item takes a point of both.
Blocking can be used to defend others, in addition to yourself.
Limitations on Blocking[]
In order to block bullets or lasers or any effect that is around the speed of sound or faster, you need to have at least 6d in your Coordination stat or your Miracle dice pool. This group of fast attacks includes anyone with the "Speeding Bullet" extra attached to their Attacks Quality.
You only get to use one set per roll with some exceptions. If you take a -1d to your pool for Multiple Actions, you can potentially Block twice (or -2d for Blocking three times, etc.). If you use a Defends Quality Miracle to block which has a Duration (or longer) Extra, you can use your chosen set for each and every attacker that goes against you.
Alternatively, you can have a Shield to block with. Blocking with a Shield doesn't give you Gobble dice against fast attacks, but it allows you cover several hit locations with armor to lessen the damage (with heavy armor, you can even nullify it) against multiple attackers with a single set. Blocking with a Shield is explained below.
Blocking with a Shield[]
If you have a Shield, you can choose to cover several hit locations based on the size of the shield. A Riot Shield provides protection to 4 adjacent armor locations (often Head/Torso/Arms or One Arm, Torso, Both Legs). A round or medieval shield protects against two or three hit adjacent hit locations. A buckler can cover one location.
Note that blocking with a Shield can give you Gobble dice, but only against attacks that can be gobbled by your Block. If you are blocking gunfire (or other "fast" attacks) with a shield, then it simply provides Light Armor as cover for the selected hit locations. This Light Armor lasts for the rest of the round, against all attackers.
Block as a Defends Quality[]
If you want to have a power that emulates hyper-blocking, you would either have a Miracle (Ice Shield, Web of Defense, etc.) with a Defends Quality or a Block Hyperskill, possibly combined with a Body Hyperstat. Remember, Hyperskills can have one Quality, and the Block Hyperskill typically comes with the Defends Quality linked to it.
Hyperskills and Hyperstats can have Extras and Flaws, just like a Defends Quality. Depending on how you stat up your powers, though, having a Block Hyperskill is the cheapest way to do it (since Hyperskills are 1/2/4), followed by a Miracle with the Defends Quality (base 2/4/8 per die, with flaws reducing it to a minimum of 1/2/4), followed by the Body Hyperstat (base 4/8/16 per die). But obviously, the Body Hyperstat is more useful (applying to a number of skills), making it worth more anyway. Also, the Defends Quality on the Block Hyperskill typically cannot have a Duration/Endless/Permanent extra, at least not in the same way that a Miracle with a Defends Quality can have these extras (Up to GM approval, of course).
Some extras are more useful than others, when it comes to Defends. Duration/Endless/Permanent extras allow you to use your chosen set against every single attacker that attacks you individually (instead of just one set versus several rolls).
Adding the Interference (+3) Extra allows a Defends Quality to gobble dice BEFORE any other action takes place. It's like an uber-version of "Go First", making Width irrelevant. In fact, with the Armored Defense flaw, it makes that Defends Quality the equivalent of Heavy Armor (explained below), instead of a Block.
Armor[]
There are two types of armor in One Roll Engine, Light and Heavy Armor. In addition to this, there is mundane armor and powers that mimic armor.
Light Armor[]
Worn Light Armor reduces all Shock damage to 1 point (even one point of Light Armor does this). If the target takes Killing damage, the Light Armor converts a number of Killing damage points into Shock damage points equal to its rating.
Light Armor on inanimate objects works a bit differently. It nullifies ALL initial Shock damage, while converting Killing to Shock damage as usual. Light Armor as a Miracle power typically works this way as well (as Miracles tend to produce inanimate shields or bubbles to protect the target).
A Miracle with the Defends Quality can emulate Light Armor by taking the Armored Defense flaw with a Duration extra of some sort. You can make this Light Armor immune to Penetration by taking the Hardened Defense extra.
Heavy Armor[]
Heavy Armor reduces the width of all attacks against the target individually, subtracting its rating from each individual attack. Only an attack with high Penetration or an exceptionally wide roll will penetrate the armor. Man-portable heavy armor is too bulky for general use unless you are in a futuristic campaign with Power Armor. However, this is the kind of armor found on most vehicles, walls, and tanks.
A Miracle with the Defends Quality can emulate Heavy Armor by taking the Interference Extra and the Armored Defense flaw at the same time, along with a Duration extra of some sort. You can make this Heavy Armor into Hardened Heavy Armor immune to Penetration by taking the Hardened Defense extra.
Penetration[]
Penetration applies to both Light Armor and Heavy Armor simultaneously, unless that armor is hardened (very rare unless it's a Miracle or Talent power).
A Defends Quality with the Hardened Defense extra is immune to Penetration.