They're off to the far right of the XMB, on your user card. Or you can go to the games bar, and the trophy list is two up from whatever game you have in the drive.
The PSN ID is if you have a PSN account, but you can have a PS3 user id that isn't linked up to the PSN. They're usually the same thing though.
The log in id mainly has to do with your gamesaves, but if you've got a PSN id, it's going to be attached to a single log in id. The PSN id keeps track of trophies, and store purchases.