I want to like pvp....
Picking a build and watching top streamers play would be a good start.
Hmm, not sure where to start or what you are looking for in particular, but a couple of basics are that you only need one player to cap a point (doesn’t cap faster with more players), as a thief probably try to avoid prolonged battles in aoe heavy team fights, get in with your burst and get out, or always try to be in fights where you outnumber the enemy, try to learn a bit about rotation between points. There are a few threads recently about that with videos and stuff, check it out.
What is it in particular that is hard to get your head around?
Well understanding other classes abilities is kinda hard for me, that just takes practice and looking and playing other classes. But with wow you can have so many addons that help with pvp and i guess with GW2 you only have visual ques of whats gonna happen and i just gotta get used to that i suppose.
You’ll find a lot of thieves in 1vs1 custom arena. Go there and spectate.
Gl