You can join the chat room, but can't actually read or type any messages. It's also true that you can't access the rules page, and you can still delete posts on your wall. You can't edit your wall (I tried), or edit/use any other privileges (such as upvoting, downvoting, selecting as Best Answer, etc.) Besides the chat room, you can see the whole website. The only difference is that when you try to do one of the actions mentioned previously, it will say "You do not have permission to perform this action" or something like that. It's mostly just like when you first make an account here and you don't have enough points to do anything.
Source - I'm banned on my other account. I can provide screenshots later if you guys want.
edit: I'm pretty sure I got kicked from the discord server when I got banned on DB because I'm not in it anymore, but I'm almost positive that pokemon db showdown bans are different from pokemon db bans; I definitely remember being banned on one and not the other at times.
