if you read
this sticky, you see what you should
do to post.
anyway, the top menu (Faq|Search|Members|Chat|etc.) holds
a button called [Profile]. click that.
under the tab [Profile], there is a possibility to fill in
something in the "Location" field. do that.
under the tab [Profile] is also an option called [edit Avatar].
here, you can upload/link to an avatar.
funny you don't know how to do those things, but you do know
how to add a signature?