Banners

Okay, I was wondering how you make a layout with a banner, I have the picture that I want for the banner, I don't want any text or anything on it, I just want to know how you put it into the layout... if y'all know what I'm talking about. If this doesn't let you comment, just go to my profile, mmkay?
I'm like really lost here. I'm currently writting a story and I want a banner, but I want to make it myself so I know it goes right.
So please, please, please tell me how I put the pic into the layout description or whatever.
Thanks guys.