Don't worry I asked the same thing two weeks in.
Go to your User Control Panel, Go to "Edit Options", then scroll all the way down til you see "Change Avatar." There's literally thousands of choices, but most of them come from anime. Of course, you can upload your own avatar picture. See if you can post your own picture on there.
To get a signature, you go into "Edit Profile". Might as well put lots of filler in there anyways.
The signature text box is not way too hard to find.