It's no different than any other internet forum, best as I know. You should be able to edit your avatar via the User CP up on the left side up top (next to FAQ). Images need a host application (I use photobucket); from there you can get the proper HTML tag to copy and paste into your post, and presto - an image appears when you submit reply.
Most people who list their equipment (including myself) do so as part of their signature - again access this through the User CP and click 'Edit Signature'.
You didn't ask, but you can also insert hyperlinks to other threads where you have started a photo gallery of your system, web pages, etc., if you should choose.
I'll instruct you how to do the thank you - see that little 'Thanks' button down at the right hand lower corner of this post? Go ahead and click it and see what happens.
Seriously though - hope this helped.