How do I fade out edges?

Hi, sure this is a dumb question but I don't know how to fade out edges. I have a jpeg with solid edges, that I want to fade the bottom out into a dark background. I've trawled through all the menus trying to figure this out and I'm sure it's really easy but I can't find it. If anyone can talk me through it, I'd be so grateful.

Thanks xx

try using layer mask,and use black to white gradient in it .And adjust with brush at low opacity.

i just remembered for just fading the bottom , u go to channels make a gradient becoming black gradually ie) with different levels of grey and load it in layers press delete.
good for blending just the edges

Well I've tried to do what you said but I must be even thicker than I thought cos it was mostly double dutch - sorry I'm a bit clueless with layers, I guess I shouldn't really be trying! Aah well, thanks for the help x