What are file tabs ? File tabs are the tabs at the bottom of the editor see image below.
You can click onto the file tabs to switch between your open documents. But you can also click on them with your right mouse button so that you get more options you can see them below.
With this you can close a document or all documents, you can preview a document or you can choose to hide the file tabs if you don't wish to use them or to make more space for editing.