If you want to use Task Manager to close a program that is frozen/not responding you first need to know how to open the tool.
Here are a few ways to open Task Manager -
Right-click the Taskbar and click on Task Manager.
Open Start, do a search for Task Manager and click the result.
Use the Ctrl + Shift + Esc keyboard shortcut.
Or use the Ctrl + Alt + Del keyboard shortcut and click on Task Manager
Once the task manager is open it will look like this
Next click More details
Select the program you would like to close
Click End task