To post pictures you will need an image code.
The easiest way to post pictures on here is to go to a photo hosting site like
http://www.tinypic.com (free, no registration required)
http://www.photobucket.com (free, registration required but has neat little perks like easy resizing, private albums)
http://imageshack.us/ (I have no experience with this one)
register if you need to then upload the photo from your computer. Then make sure it's the correct size for this site (nothing larger than 640x480 I believe, on the main forums) then copy the image code (starts out:
) and paste that into the box you type a message in to show your picture off.
I have step by step instructions located above. If you need further help please feel free to private message me.