Hey Adam, the first place to start is with my How to Install a MIDI Controller in FL Studio tutorial.

Here’s a quick explanation of how to install a MIDI Keyboard in FL Studio:

1. Install drivers for your MIDI Controller from the manufacturer’s website
2. Plug the MIDI Controller into the computer and turn the controller on (if it has a on/off switch)
3. Inside FL Studio, go to your MIDI Settings (F10)
4. Make sure to enable your MIDI Device under Input
   1. Under Input, click the device to highlight it
   2. Then click Enable

Don’t worry about the Output.  For a MIDI Keyboard connected through USB you just need to focus on the Input section.   Output is if you’re wanting to control outboard hardware or sound modules.

If you’ve enabled it properly.. then it comes down to that particular MIDI Keyboard you’re using.

Is there a certain mode you should be using?

I haven’t used the Novation FLkey MIDI Keyboard for FL Studio.. so can’t give help on specifics..

At the time of writing, I currently use and recommend the M-Audio Oxygen Pro MIDI Keyboard to students of my platform here!