What does enchanting an item do?

When you enchant an item, it applies a bonus to it. This bonus can be anywhere from 5% to 35%, depending on the level of the item. This bonus percentage adds to the chances an item will hit or miss, or, in the case of armor, be hit or be missed. It may not sound like a big deal, but anyone who has forgotten to enchant a brand new weapon, and loses to a blue-con mob because they can't hit the damn thing, knows how important it is.

Incidentally, armor bonus percentage cancels out weapon bonus percentage. So if your weapon has a 15% bonus, and hits a piece of armor with a 10% bonus, you will only receive a 5% bonus to your chance to hit. And of course, in the frontiers, all those level 50s are running around with 35% bonuses on armor and weapon, so if you don't have that bonus, you have a huge disadvantage.

Don't forget to enchant your legendary weapons!