And I know that I shouldn't be doing this on a shared
account, but I'm just playing around.
Buddy, if you "shouldn't be doing that" then "just playing around" is no excuse.
Unless you have root on the machine, adduser won't work. And passwd doesn't accept a password on the command line (it would be a huge security breach if it did), you'll have to use Expect;
As for the rest of your questions, they depend on the details of how the server was set up, and this is not the place to discuss them. You want a unix discussion forum. Go back two routers and turn left.