Editor add-ons enable user interaction through customized menus, dialogs, and sidebars. The following links provide information building these types of interfaces.
Add-on menus are created using Apps Script's base Ui service. Menus items provide initial starting points for using your add-on, but you must design them to take into account the add-on authorization lifecycle.
When building HTML interfaces for editor add-ons, you should use the editor add-on CSS package to help your add-on look and feel like the G Suite editors they extend.