Up at the top, just undernearth where it says "Board Index", it says "User Control Panel". Click on that link to go to your... you guessed it! Control Panel
There are tabs for editing different things : Overview, Profile, Board Preferences, Private Messages, Usergroups, Friends & Foes. Go to the Profile tab. There are 4 things going down the left side. "Edit Signature" will let you put what you want to show up at the bottom of every post. "Edit Avatar" will let you add the small picture under your username. You can upload a picture from your machine, or from the internet (but only if it's free for use, or the picture belongs to you.)
If you need any more help, just ask!