Hello souleater2356! To edit your signature, scroll to the top and along the bar is a Profile button. Click that and then click on Forum Profile. Scroll down a bit and there'll be a box to enter your signature.
To put an image, copy and paste this code into the box:
[img]PICTURE URL HERE[/url]
Replace the 'PICTURE URL HERE' part with the code of your picture.
Hope that helps!
haha ferretfoo beat me to it!