Okay, I'll try and talk you through this (If I don't make any sense then it would be my fault not yours... I'm bad at explaining things).
I'm sure you already know how to get to
Main, so I don't think I'll need to tell you how to get there. When you are there, there should be a bunch of little images above your text box thing. Right between the pictures of an anchor and a brush is an image of a tree (it should say
insert/edit image when you hover over it). After you click on it, it should come up with three things:
Image URL,
Image Description and
Title. Just paste the URL (image address) in the first bar, a short description in the second bar, and the title of the image in the third bar. After you're done with that, just click on the
Insert button. I hope this helps.