Initial Setup
Set your MPK device to the FL Studio preset by pressing Prog Select and the corresponding pad. On the MPK Mini Plus, which we are using for this tutorial we will use Pad 4.
Next, in FL Studio, navigate to Options>MIDI Settings 
Then, highlight MPK Mini Plus, and MIDIOUT2 in the output section and choose Send Master Sync. Note: for other MPK controllers, this will look different, you may only have MPK mini MK III for instance, if that is the case, there is no extra MIDI port on the device, and you only need to complete these steps for the MPK ports that are visible.
Next, in the input section, highlight the same ports, and select Enable.
Next, you will want to refer to your MPK's User Manual for setting the Clock/Sync source. If Note repeat and the Arpeggiator are not in time, this is your issue. The clock-source must be set to EXT in orderfor the MPK Mini to receive tempo data from FL Studio.
On the MPK MINI Plus, hold Note Repeat, and C#3 labeled Sync, then use the encoder knob to set the BPM to EXT.
Easy Pad Set-up
Now, you should be able to load a virtual instrument, and when you trigger a key on the keyboard, it will play that instrument given that it is selected.
If you would like to use the Pads to control multiple different drum samples, the easiest way to do so would be to load FPC.
Select Add, and then select FPC:
FPC is FL Studio's MPC-style sampler instrument. Your pads will automatically be mapped to those on screen, Bank A covering the bottom 8 pads, and Bank B, the top.
Advanced Pad Set-up
Next, we will go over a more advanced setup, so that you can use the pads to control multiple Fruity Samplers at once.
Here, we will use FL Layer to create a layer channel to send MIDI to multiple Fruity Sampler instances at once.
Choose FL Layer from the Add menu.
Here, we will use 4 samples, a Kick, a Hihat, a Clap, and a Snare.
The first step is to limit MIDI information each sample will respond to.
Click on the FL Sampler with the Kick assigned and go to the wrench icon.
Then, trigger the pad on your MPK Mini that you wish to place the Kick sample on, you will see it light up. You will notice that the pitch is much lower. Find the key that is lighting up on the on-screen keyboard and right-click it to change the root note. This will return the sample to its original pitch when that pad is triggered.
Then, left-click to drag the MIDI range so that it only includes the note you wish to assign the sample to.
We will want to complete the same process for the rest of your samples. If you require more than 8, select Bank B on the MPK, and repeat the steps in the same fashion.
Once you have completed this, you will want to open Fruity Layer, and highlight all of the FL Samplers that you just edited and choose Set-Children.
Now, as long as you have FL Layer Selected, you will trigger the samples you have selected as children.
