Adobe After Effects why are the layers greyed out

It's a bit like trying to learn how to drive but frustratingly you can't find where the ignition is but what I need to do is start creating layers.

This should be as easy as right clicking in 'Timeline' at the bottom.



However if this isn't working and when you click on > Layer > 

the dropdown here is all greyed out then you probably need to click on 'Create a New Composition' first.