Need help with fade in layers ect...

Hi I am working on my website and now I am at the stage to add javascripts.

I downloaded jquery and I am trying to make a image that when you double click on it. It will show a hidden layer which will fade in showing a photo album. Then when the users mouse of not over that hidden layer it fade out.

I need an examle of this or at least need to look at someones script that done such a thing .

I am trying to fade in and out div ids if that is not right.

then explain to me if I have to use classes so I can specifie how each layer shows. So that I can have more than 1 at different areas for different purposes.