Light beam implementation in Slicer has not been completed yet.
The main interaction is grabbing and moving objects. It may not seem to be a lot, but it is actually very powerful, as moving an object modifies the associated transform node. Transform nodes can be used to move all objects, such as markup nodes, which are used as inputs by many modules; you can reslice volume (using Volume Reslice Driver module in SlicerIGT extension), you can also put multiple objects under the same transform in the scene to create groups; you can exclude objects from (disable selectable attribute), etc. You can get access to current position of the headset and controllers.
In addition to using transforms with you can also add observers to transforms and implement your own custom behavior. This is used by one of the forum members to implement segment editing in virtual reality.