How you can close apps, depends on your launcher. On the rM1 most launchers depend on using the buttons. On the rM2, only remux currently supports gestures.
Draft expects either the application to allow exiting from the UI, or for the user to use an external service (button-capture or genie) to manage closing the application.
Hold the middle button or swipe up the side of the display to open remux and switch applications.
You have several options with Oxide. The Oxide usage documentation has more information.