Layers are containers for html that can be layered on top of each other. They allow control over position and can be controlled with behavior. A layer can be made to visible or not, it can be dragged or programmed to move with javascript.
A layer also has a tag property which is best left on DIV if you wish to use layers for static layout. This will set the style attribute of the layer to position:absolute. This means the layer will stay precisely where you placed it on the page.
These are the main initial properties that you set.
If you wish to make a layer dragable then add a drag layer behaviour to the BODY onLoad event