I animated these 3 layers and than tried combining but couldn't do it. I know how to combine rendered images from different layers in compositor but I'm trying out animation. Please help.!!!
First make sure that you enable transparency for the background (so that all of the layers have an alpha channel.
Then combine the layers in the compositor using Alpha Over
For a more detailed explanation Read:
My objects are semi-transparent, and not one behind the other in the compositor
and Can someone explain the layer system?
You can shift + Left Click on the Layers at the bottom panel to select which to render.
If you need more advanced control on how to combine them you can composite them together using render layers.