I was under the impression that Discipline was more aimed at PvP cause of the damage blocking but i've seen it work in cata heroic.
First step for healing, get Healbot Continued and set it up, makes healing way easier imo.
Second you need to find a priest and have a look at their gear Wrmry
is a Holy priest, so have a look at him
Third when you hit 85 yell in /g until you've got a guild group to help you through dungeons. And if you want to try healing a raid, try get on a BH group