There are multiple ways of copying layers:
To copy a layer, right click on it -> select Copy -> Layer.
To paste a layer, right click where you would like to have it -> choose Paste -> Layer(S).
You can find the previous copy/paste options within the "..." layer menus too.
Ctrl + C, Ctrl + V
Select a layer and you can use Ctrl + C to copy it and Ctrl + V to paste it.
Structures, like rows and columns can be copied too. This will copy the layers inside them as well.