Don't feel stupid at all, Fan Forum is super confusing at first. To have a custom icon/avatar you have to have at least 100 posts, but until then you can use standard ones which are under 'User CP' at the very top of Fan Forum's site page. Then under 'Settings and Options' you choose 'Edit Avatar' and you can choose one there.
As for a signature - the words under your message - you would go to 'User CP,' then 'Edit Signature' under 'Settings and Options.' And type in whatever you want it to be.
Hope that wasn't more confusing than helpful. Feel free to ask if you still have trouble.
