First, you have to host the your pics someplace. That means they have to be on a server that can be accessed thru the web, and each photo will have a unique address, something like this (see example).
You can just type it in like that (or copy and paste) and leave it, so when we click on the link, also called a URL, we'll see the image. Or if you want to actually display the image in your post, you'll need to add "image tags". These are the tags used before [img] and after [/img] the image address (URL). There are two ways to add them. First you can just type them in, at the beginning and end, or you can highlight the URL and click the Image Button at the top of the posting screen. The program will automatically add the tags to each end of the URL. Remember not to leave any spaces between the URL and the image tags, or put any periods or commas at the end of the URL addy. When your finished, you'll end up with this.
Not all host allow linking, so you need to make sure the one you use does. Imageshack and Photobucket seem to be the most popular.
Please keep your images to a maximum of 600 x 450 pixels.
Remember that some folks are on dial-up, so inserting dozens of pictures could kill them when they open a post, therefore please limit your post to six (6) images.