Here's the Reader's Digest version of how to post pics in a message.
1. Upload your pic(s) to a free host site, such as Photobucket.
2. Next to each pic is an IMG box. Left click in that box and the contents will automatically be copied onto your clipboard.
3. Paste those contents into a message on here.
4. It is not necessary but if you want to see if it worked before posting your message you can click on the Preview button.
Hint: If you think you might be using Photobucket for eventually storing lots of pics it is a good idea to create different folders for each theme such as Food, Hobbies, Cars, etc. Just make sure you upload them to the appropriate folder. Keeping your Photobucket pics organized makes them much easier to find later on.