Most VR or XR applications require controllers to interact with the virtual content. Hand-held controllers allow you to interact with certain objects within the application, such as “touching” something in virtual reality, picking up a virtual object, or interacting with objects with your hands or fingers in other ways, just as you would with your hands in real life. The VR controllers come in various shapes and designs, with varying levels of user ergonomics and precision.
Sometimes, controllers are not required as certain VR devices have built-in hand-tracking capabilities. This will enable you to extend and use your hands to select objects instead of using separate handheld devices.
Varjo headsets work together with all SteamVR™ compatible controllers. You can use one or two, depending on the needs of your application and its interactions. You can find more details on supported models and their compatibility here. Note that Varjo XR-3 and VR-3 headsets have built-in Ultraleap hand tracking, so you can use your hands to interact with virtual content. Varjo Aero does not feature built-in hand tracking.