The Hue Dimmer switch can be used in two ways, depending on whether you have a Hue Bridge and the Hue app.
When purchased as part of a set with a Philips Hue light fixture, the Dimmer switch functions in standalone mode. This means that it can control the lamp or light fixture with which it came, including turning on/off the light, dimming, and brightening. If the Dimmer switch was purchased with a White ambiance or White and color ambiance light fixture, you can also cycle through four preset light recipes, including Read, Relax, Energize, and Concentrate. It is not possible to control the color of the light beyond the preset light recipes.
Connected to Hue Bridge:
For more functionality, you can connect your Dimmer switch to your Hue app and Hue Bridge. When paired with your smart lighting system, the Dimmer switch can control up to 50 Hue lights in up to two Rooms. You can also assign your own preferred scenes to cycle through.