In order to add the speech boxes and text, you have to use an image editing program, such as Microsoft Paint or Adobe Photoshop. You can see my instructions for posting pictures here.

A url is basically an Internet address and is in the form of http://www.ldw.com (a very simple url example). Every Internet page has a unique url, and the url that the forum is asking you for is, in essence, the Internet address of your picture (see the post I referred to above for more information).