Task Manager in Mac OS

Task Manager is in Windows computer, for computer running Mac OS the name is Activity Monitor.

To Run Activity Monitor :

Press Command + Space bar, it will show the Search field.
Write Activity monitor in search column, then you will see result Activity Monitor, click it to run.

Other way:
In Main screen/desktop, Choose Go menu, then choose Utilities, then you will see the Activity monitor

Example to force stopping the application: Select the App, then click x sign, it will force closing/quit the application..