First you'll have to upload your images to an image hosting site. We have our own hosting, over in the bragging board, but imgur.com and similar sites will also work. Create an album, select the upload picture option, then follow the prompts. Once you do that, you can create a post and add images to it.
Pull up the picture you want to add, then right click on it, which will pull up a small menu. Depending on your browser (Internet Explorer, Firefox, Google Chrome), you'll either click "Copy Image Address" for Chrome, or Properties for Internet Explorer. If you click properties, copy (control + c) the url address.
In your post, paste the image url in between image tags: "[img]" and "[/img]", with the brackets but minus the quotes. If you're not sure whether you did it right, hit "Preview Reply" and see if the image pulls up.
Formerly TN Lone Wolf
"We are only as strong as we are united, as weak as we are divided." - J.K. Rowling