Enchantment
Bonus
Bonus is the level of enchantment applied to the piece of equipment you are using.
For weapons, a 10% Bonus means an extra 10% chance to hit (applied to your current chance to hit.) If you have a 50% chance to hit something, you now have a 55% chance to hit something (not 60%!!!). It's 10% of your current chance to hit, not just an extra 10%.
For armor, a 10% Bonus means an extra 10% chance a monster will miss you on that particular body zone. Again, it's applied to the monster's current chance to miss you, and not a straight 10% increase.
For shields, a 10% bonus means an extra 10% chance to block, again, that's applied to your current chance to block.
Let me tell you why they are applied percentages, and not just added. I believe the highest level of enchantment to be 30%. It could possibly be a little higher or lower, but I guarantee the highest level to be no less than 25%. Now, assume there's someone who can use a large shield (10% base chance to block) and he has 50 skill in shields (adding 25% chance to block), and he has a shield with 30% enchantment on it. It can't be added because that would give him a 65% chance to block. It's multiplied - giving him a 45.5% chance to block ((10% + 25%) * 1.3), which is still very high, but it's not 65%. Many people have said that bonuses are added, but they are not - they are multiplied. Please keep this in mind.
Getting items Enchanted
1) Any merchant or player crafted item can be taken to an enchanter and enchanted to add bonus to it, but the piece must be of a certain material. Typically, the lowest 3 levels of materials you can buy from a merchant can not be enchanted. After that - the 4th level of material gains a 5% bonus, the 5th level gains a 10% bonus and so on. We know there are at least 8 types of material for a given item, meaning there's at least a 25% bonus out there to be had, but I'm pretty sure there's also a 9th type of material that cannot be bought from local merchants, and I'm going to guess there can be a 30% enchantment applied to it.
2) Items that come from monsters can typically not be enchanted. Most of the time, monster dropped items will already be enchanted, (albeit a low enchantment compared to what it *could* be).
3) Enchantments are forever, kinda like diamonds. Once enchanted, something can never be unenchanted, nor can it be multienchanted. There is no way to disenchant your armor, nor reenchant.