Alright, the DC (difficulty class) seems to have been adequetely explained above, but as a summary, people roll a 20 sided die, then add that number to the save the DC applies to (be it fortitude, reflex, or will). This is why I never use items with a fixed DC (one unchanged by my stats) as the enemies usually resist it no problem later on.
As for damage resistance, the "5/-" means that the first 5 points of that specific damage is ignored. So if you have 5/- vs energy weapons, and a lightsaber would normally do 30 damage to you, it now does 25. I believe this is the same when it says +3 vs. energy, though I am more familiar with the slash minus format.
