After powering your console for the first time, or after resetting the console, or after a software update, there will be no fixtures patched. This means your channel faders will not be controlling your rig, as currently the console does not know what fixtures you may have.
If you connect RDM enabled fixtures to your FLX S24 or S48, they will automatically be discovered and patched, thanks to RigSync. If you wish to automatically discover RDM fixtures on FLX, tap Setup -> Universes, and enable RigSync under Remote Device Management.
See the video for more information on RigSync.
If you don't have RDM enabled fixtures, you will need to patch your fixtures manually. This means you need to tell the console which fader you want to control which light, and how. This is done by pressing Setup -> Add Fixtures. This takes you to the screen pictured, where you will be able to find the required fixtures, and tap Next >.
After tapping Next, you can then tell the console how many of these fixtures you want, the fixture number/channel fader number you would like to control these lights with, and the DMX address of the first fixture. If you wish to patch multiple fixtures at once, and they are not addressed sequentially, use the patch offset field.
You can then tap Finish, and the console will patch your fixtures. This will show you the fixture schedule, with your new fixtures listed. This is where you can edit your fixtures, such as give them custom names.
You can then exit Setup, and you will be able to control your lights.