You get training for it starting with practice runs at the NOSC (we had a practice coffin for the flag folding, including how to deal with common mistakes on the fly) and there's an official video too (but no NKO, thank goodness). Next, guys go along and watch from the van a couple times. After that you "play" the bugle a couple of times, posted a short ways away from the gravesite (the distance helps a lot for people who get stage fright). Then finally you are the assistant folder. The lead folder is the one presenting the flag and reciting the spiel to the recipient.
Don't take my word for it but I think you get paid a drill starting when you go along in the van to a service, since you're technically part of that detail.
The expectations are that you're always on time (your show time is something an hour before the party's scheduled time to arrive) and your dress uniforms are squared away (no old, dirty ribbons, no wrinkles, good haircut, etc.). I think there is a small uniform allowance though, but don't take my word for that either.