To turn a device on or off, or dim, please make sure you've claimed a device and it appears on your dashboard.
To turn a device on or off, simply tap the device as it appears on your dashboard. To Dim, simply move the slider to the desired level. If you have a non dimmable device you will not see the dimming slider.
If you are viewing the device's details, just tap the On/Off button. You can also dim compatible devices by using the slider to control the dimming level.