I was in your position until half way through Cata. So I can appreciate the steep learning curve once you hit max level....everything is different.
I agree with the previous recommendations. I also agree that DPS in greens doesn't matter. I usually go to www.wowhead.com
and do a gear search for cloth gear and try and find the highest gear I can get through questing. I go find that quest chain and complete it. But while working on the quest chain I cue up for random dungeons. That way your's not just sitting around or questing randomly.
Once you have max gear through questing start working on dailies so you can get some faction gear. I recommend starting with the Golden Lotus and Shadow Pan. They are pretty easy to quest as shadow and really help you get a feel for your rotations since they have "boss" fights at the end of each string (once you are "friendly" with the faction).
I pretty much continue this behavior and keep upping the hardness of the dungeons I cue for as my gear allows and eventually you will be able to cue for "LFR"- Looking for Raid and you will see what raiding is able and have fun doing it.
As for PVP.....well at this point its all gear based. You need to make/buy a full set of tailoring PVP gear and then start doing BGs for honor. However, I will say that as a priest you may find your more help in a BG as a healer....(just food for thought). Anyway, most importantly welcome to H2P and have fun playing (that's the most important thing in the end).