You need to download either PSP (Paint Shop Pro) or PS (Photoshop) i'd recommend PS,then you can just read tutorials and learn things and improve,if not and just want a banner then request a banner in the thread above.
+ Once you have your banner you need to upload it to a host. www.81x.com is the only one I can think of right now.
+ Then copy the URL of the image (Right-Click, Properties, Image URL)
+ Go to USER CP on the top of the forums > then options, and under signature type [*img]URL[/img].
Make sure not to put that Asterik * there in the real thing.