To restart an app on a Samsung Galaxy phone, press the three vertical bar button, swipe up on the app to close, then relaunch that app from the app drawer or home screen. On Pixel phones, swipe up from the bottom, swipe up on the app to close, then reopen that app from the app drawer or home screen.
Restarting an app on your Android phone allows you to fix frozen apps and other app issues as well as bring your changes in the app into effect. Quitting and relaunching an app is easy, but it varies slightly depending on your model, so we’ll demonstrate on both a Galaxy and Pixel phone.