Hey draquish not everyone is a computer elite like you...
What you need to do is find a small picture like the size you see people using. Upload it at a website like
http://www.imageshack.us and copy the link (for imageshack the best to use for signature pictures is the very last one they list). Then you come back to this site with the link copied, go to your profile, and find where it says "signature" then paste the link there with [img]before%20it%20and[/img] after it. Then your picture will show up after each post you make.
If you want a picture like the others have, you need to either crop a pre-made one, or make one of your own.