If you want to post pictures you have on your computer, you'll have to upload them to teh internetz first by using certrain upload sites, like imageshack.us. They will provide you with a link that you can post here (mind to resize). If you want to post a picture that you found on google or any other site, copy its URL (right click on the picture; properties), and post it here using the IMG tags around the url.
Once again, don't forget to resize if needed. ( [img width=680] )