Please search before posting questions like this... this topic has been covered a hundred times. Also, as it is not a cosmetic question, it doesn't belong here. I'm trying to be nice, but does anyone even read the stuff I post? There's two stickies at the top that tell all about what this forum is for.
Now, to answer the question. You need an online image host of some kind. I use www.printroom.com , personally. It's free and you get gobs of space. It's got its downsides, like the fact that they resize large images and put a banner at the top. Upload your pictures, and figure out the URL of the image (the host will usually tell you beneath the picture). Now, insert the URL between [IMG.] and [/IMG.], but don't put the period in the IMG tags. If you format it correctly, it will show up.