Adding screens in Editor is simple. While in Editor, just click the Add button in the top toolbar.
It will display templates in your libraries that you can use to jumpstart your new screen. Click on the template you would like to use for your new screen. You can add a new screen with a template with a keyboard shortcut - [Ctrl] + [Alt] + [N] (Win) or [Cmd] + [Opt] + [N] (Mac). Once you've selected your screen type, press the New Screen button.
Note: changes to a template in a library do not affect screens that were created using that template.