what is a pre-board appointment?

Like an on-boarding? Where you receive paperwork, take your picture, stuff like that?

yes, all they said was I was going to need to bring my paperwork and licenses and get my employee picture taken. But I don't know if I need to wear something formal or if I can just wear scrubs?

Right about now is a good time to learn about appropriately asserting yourself. All of your questions would most appropriately be answered by someone at your new facility. Ask them. Wouldn't you hate it if one of us gave you a bad guess at what you "should" do/wear? Most of us don't even have a clue as to what/where "Banner" is.

I wore scrubs to mine at my first job, and pants with a tank and a jean jacket to my second one. Just look clean, I suppose?