I know, you’re amazed at my name. The early bird gets the worm 
I’m level 51 and wondering what part of BRD is first. Like what do I say in lfg? Arena? I know it’s recommended to be level 52 to start but I’m a damn good holy pally. It’s what I played in vanilla.
Just say healer LfG BRD.
And then I get invited only to find out they are doing emperor?
I would try and get to 53-54. Then you don’t have to worry about what group you get into. But you’re probably better off making your own group if you want to go further than the golem lord. It can be hard to find a pug group that wants to go the distance in BRD, you will likely have to rely on your guild if you want to do it in a reasonable amount of time without the group falling apart. You will likely have multiple times where a melee class/hunter that joins your group and once you get to arena/anger they bail because they didn’t get their item.
But you first want to get the shadowforge key quest done, this lets you unlock the rest of BRD.
If you’re after BiS google whatever spec your looking for. wowhead classic lists out everything and tells you where to get it.
If you’re looking to just level then do whatever.
If you google something like “what kind of brd run should I do” you’ll find reddit posts that explain all the different runs you see in lfg.