Weapons generally degrade slowly and standard weapons are easy to keep above a 75% durability condition. Rarer weapons are harder to keep working but this can be mitigated through selective play.
The Power Level of an item is used to calculate your overall power (the average of all your equipped gear), which can affect how much damage you give and take.
Your Specialty allows you to do extra damage to entities. Your specialtiy depends on the class that you select at the beginning of the game.