To benefit from all the rich features of the Hue ecosystem and the Philips Hue app you will need a Hue bridge. The most straight forward way to do this is to open the Philips Hue app, add your Hue dimmer switch via the 'settings' menu > 'Accessory setup' > 'Add accessory' > 'Hue dimmer switch' > 'Option 2' and follow the instructions. As soon as your Hue dimmer switch is found all your Hue connected luminiares recognized and visible in the Philips Hue app, ready to be controlled. Alternatively you can add your Hue connected luminaires by manual searching for new lights in the Philips Hue App. Got to 'Setting' > 'Ligh setup' > 'Add light' > '+ Add serial number' and follow the onscreen instructions.
Note: That this requires the unique six digit S/N number for your Hue connected luminaire which is provided with the product, but also can be found near the connection terminals inside your luminaire.