I know how to post an image on the forum, it uses the [IMG]url of the image[/IMG] code. But I don't know how to make that image into a link. Could someone help me out? And what is this form of code called?

[ url= stick the url here][ IMG]url of the image[ /IMG][ /url]
no spaces obviously.

It's called bulletin board code, BBCode for short

If you want to post an image on HTML there are so many facilities can be available such as bulletin board, BB code and so on are useful for the image for HTML there are so many advance facilities are there it can described so many things which is really great for HTML.