Applications on the HoloLens are launched from the Windows Home menu.
Launching an App
To launch an app from the Windows Home Menu, open the menu by tapping on the Windows icon on your wrist and then tap the All Apps button to show all apps installed on your HoloLens 2. Scroll down and tap the app tile to place the 3D tile in your space. Tap the Play icon within the 3D tile to launch the app. You can hover over the app tile and tap Pin to pin the app to the default screen of the Windows Home Menu.
While you are not in the app, you can close any instances of the app that are running by tapping the Close icon in the corner of the 3D tile. The 3D tile will be located wherever you last launched app.
Open the Windows Home menu by tapping the Windows icon in your wrist, then tap the All Apps button to view all installed apps on the HoloLens. Hover over the app tile you wish to remove and tap Uninstall.