Check out the FAQ tab at the top right of the page. From there you will find a link giving directions for some general forum functions....
Click on -> FAQ Scroll down to "Reading and Posting Messages"
A quick and dirty answer....
You won't be able to just upload a picture to post unless you upload it to an album in your profile. Try setting up an account at a place like photo bucker Photobucket.com.
After you upload the pictures there, you will have a URL available for the picture. Using Photobucket, they will give you a URL in