Help with phone drive app on iOS.

iOS and iPadOS
I was wondering if someone could give me some tips on the phone drive app for iOS? I listened to Carla's great podcast but am still confused about some things. Can you put a whole folder on phone drive? When I pressed the add button, I saw two text edit fields, untitled folder and another text field below that. I was wondering what the second text field was for. Also how can you add a PDF document to the phone drive? Thanks for any help members can provide. I also would like to put all of my music on phone drive, because I dislike iTunes very much. Thanks again.