Expect a conversation about yourself! I know that sounds daunting (I know I always blank when telling someone about who I am...), but I'd liken it to you meeting someone for the first time. So, the other person is just trying to find out more about you. You know, you talk about your interests and hobbies, some stuff you do in school, what books you've liked, etc. I've heard of "quirky" questions being thrown at kids, but I didn't get one in my interview. Trust me, the hour goes by really quickly...TOO quickly...
I wore normal clothes...Jeans, sneakers, a t-shirt, a jacket...It was REALLY low-key.
You'll be fine

Once you get into a nice groove, your anxiety will melt away like butter over a freshly toasted bagel. Yum...