Congrats! You just need to show up. There will be volunteers guiding you along the way so no need to be nervous (i know easier said than done!). Just plan for worst case scenario of having to wait a few hours in line so bring water, weather-appropriate clothes, and something to keep you entertained while you wait (book/ phone/etc). Bring your id and check to make sure you don't need anything else in your state.
Best of luck!
Edit: and not everywhere is bad with lines. Some places are in and out
Ceo at my old company made us dress up super professionally, but he frequently would be wearing shorts and a Hawaiian shirt with sandals. We didn't webbed get casual Friday or anything like that