The footage panel is used for previewing your footage. There are also some tools that work only in the footage panel.

To access the footage panel double click on the layer. However this panel is often accessed by accident. Its accessed when double clicking on a layer. You can tell you're in this panel when you see the white bar at the bottom. There are specific things you can do in this layer but we usually don't need to be in this panel. Image of the footage panel:

You will find this is a mistake that happens frequently. To get out of this panel go to the top of that panel and choose the name of your main comp. Or you can reset the workspace area back to saved layout:

Resetting this will not change anything in your project. It simply restores your workspace area to the default standard layout.