First and third-party apps in the system can be pinned on the taskbar.
To pin an app, go to the app's button in 'Start menu' ( ) and right click on the app. Select the 'Pin to the taskbar' option.
To unpin the app, right-click the closed pinned app on the taskbar and select 'Unpin'.
NOTE: Dragging an app from desktop to taskbar creates a shortcut of the app but doesn't pin it.