New to PIT picking

I did my first pick, and although I really loved driving the OP around and being alone, I still have a lot to learn. I made some mistakes already but that’s because they just threw me on pick right after my victory lap and barely trained me on the device besides signing me in. I was wondering how changing the cages works? When I left I just put it in an empty space that was close to the dock but not right in front of it since it was full, or I guessed it was (my trainer told me whenever it looks full to change it.) …I assumed that would be acceptable. I also wasn’t told what you do after as far as getting another cage. Do you have to ask for a specific one or just grab any empty one? And will I just be assigned to that same dock for an entire shift? Sorry for all the questions, the PA just seemed pretty annoyed with me not knowing things even though it’s my first week and I hate feeling like I’m burdening anyone, I just want to do my job and go lol.