There have been multiple threads already made about ateres. Just search them on the site.
From what I know, they have rules about hair. If your hair is past shoulder length, then you need to put it up for class, possibly outside of class as well. You aren’t allowed to go to hang out places after dark such as the tachana hamerkazit, ben yehudah, malcha mall or anywhere. But you are allowed to go to ben yehuda during the day. Based on what I have heard from girls last year, the rules about where you can go can be kind of annoying but even though I didn’t go to ateres (but I interviewed there) I can understand why these rules make sense. I personally bumped into guys I knew from youth groups at ben yehuda and the tachana after dark and they don’t want you to have that nisayon.