Each full screen view of the Topbar apps has the option to either close or hide the app.
Hide will restore the view of the desktop and Topbar will just take up the space at the top of the screen, with the app names displayed. To see the full screen view you have to click on the name of the app on the left of Topbar:
Close will close the app and to restart it you will need to click on the start screen icon in the top left corner to get back to the Topbar start screen as described earlier in this guide.