End Task

Closes (terminates) the currently selected process (program / application) - this is useful if the application you are using has frozen or locked up and you need to close it.

Open / Close Navigation

This opens / closes the navigation to show only the icons for navigation or icons with descriptions.

Processes

This tab shows all running Apps, Background processes and Windows processes along with how much CPU, Memory, Disk, Network and GPU resources they are using.  This view also allows you to see current Power usage for each app, useful on a laptop/tablet as you can see which apps are using the most battery power.

Performance

Shows detailed information about CPU, Memory, Disk, and Network/Ethernet/Wifi usage.

Also shows the Up time of your computer which is how long since it was last restarted.

App history

Maintains a list of application that you have launched during a session, so that you can easily switch to any previously used application, and view its CPU and Network usage.

Startup apps

Here you can manage applications and processes which start with Windows logon.

Users

Shown here are all logged on users and what processes they are currently using - you can also disconnect any user and see more information about how many resources (disk, CPU, memory and disk) they are using.

Details

This tab is similar to the Processes tab but provides access to more advanced settings - from here you will be able to end task and end process tree, create dump file, set CPU priority level and CPU affinity of selected application, search process details online, enable/disable UAC virtualization, switch to respective service in Services tab, and view selected process properties.

Services

The Services tab lists all the Windows services. It shows the description of the service and its current state and allows you to start, stop and restart a service.

Settings

Choose the default start page (tab) when you open Task Manager, this is usually Processes but you can choose any of the tabs.

Choose how often you want the information to be updated.

Chose how you wish the Task Manager window to behave e.g. always on top of other windows, automatically minimize when not in use, or to hide when minimized.

There are also some other more advanced settings relating to memory dumps but most users won't need to touch these.