To post a pic:
Hit "reply" as if you are going to post.
Under the box where you type your posts you'll see the words "Additional Options."
Click on those words.
Then you'll see the word "Attach" followed by a blank box, then a Button that says "Browse."
Hit the Browse button and find your pic. Double click it and it's name should appear in the box between the words "Attach" and "Browse."
Then hit post.