First, be sure the photos are not too big. There's a list that pops up when you click on the "Manage Attachments" button down below in the "Additional Options" box. For instance, a .jpg can't be larger than 1024x768. If yours is larger than that, you have to resize it down.
Then click the "Browse" button, find the file on your computer, double click on it, and hit "Upload". Done.
You are limited to a max of five photos to a post.