Task manager is a quick way of monitoring live information about what is going on with your machine in real time.
Task manager can be opened in a number of ways my favorite is to right click on the taskbar and select Task Manager.
Taskmgr.exe also works.
by default is only shows open programs but if you click more details you get a lot more information.
If you right click on an application you can end it or find out information about it.
The performance shows live statistics about how many resources are being used on the computer.
Resource Monitor gives and even more detailed view of this.
The users tab shows who is logged on and what kind of resources they are using.
Details shows what processes are running and information about them.
And services shows information about the services running and not running.
You can start and stop services here or open Services.msc from here.