Welcome to Android Central! Sorry for the delay. Not all devices come with a preinstalled task manager, and in general, they are not needed for Android, since the system should be allowed to handle opening, closing, and swapping apps. If you do it manually, it can be counterproductive. Task managers are mostly useful to troubleshoot a misbehaving app, but you can use other System Setting menus to force close an app anyway. See these articles for more info: