In order to put a picture inside a post, you need to have the image stored on a website. Then what you are doing is "referencing" where the picture is stored. You use the html command "img src" to do that.

If you store your pictures on photobucket.com, they provide you with an HTML tag that you can use to do that. Once your pictures are stored on photobucket (it's free), there are 3 lines listed under each picture. Using your mouse, click the HTML one and you'll see it say "link copied". Then come here and paste (Control V or use your right mouse button) what you copied. When you "preview" your message, you should see your picture in the preview version if you did it correctly.