What is DC?

DC - Difficulty Class :
     definition: The Difficulty Class is a number associated with an action that represents how hard that action is to do or resist.

This is not the easiest concept to grasp but it is part of the new RPG rules. For instance, when a spell is cast on you, you are given a DC. The DC is 10 + Spell Level + Casting Stat Modifier + Items + Feats = DC. Clear on that? You then use your (as us old timers would put it) saving throw modifiers from Wisdom, Constitution or other stat + feats + items and roll the 20 sided dice to see if we succeed in saving against that spell.

So in general, if you are an attacking type or crowd control, you want to raise your DC score in your primary attack form.

For those of us who are support types (Clerics, Favored Souls, Bards) and do NO attacking, we do not require a DC bonus as we are buffing or healing our party. There is one exception to this. Support types do need a DC to remove diseases, web, hold or any other spell that has been placed upon their party member.

Here is the DDOWIKI article on it if you really want to be confused.