Under the UserCP tab you can find a section that allows you to make a photo album. You can then upload your pictures to this site, and then place them in your post using the Insert Image button that looks like a mountain with a yellow sky above the posting box.
You can also get a free pic hosting site (like flikr.com) and upload your photos, then use the link tab (the world with a chain up there) to add them to your post. Once you've done it the first time it makes perfect sense thereafter....