Connect the USB cable to the midi keyboard and the other end into the USB port on the computer hard drive. Allow the computer to find and install the drivers needed to operate the midi controller.
Turn on the keyboard. Some midi keyboards are powered from computers, others require batteries or adapters.
Open the FL Studios program and choose "Options"; some options will need to be changed for your midi controller to work. Check the box marked "Enable Midi Remote Control."
Return to FL Studios and select "Midi Options" from the menu.
Choose your keyboard, listed in the "Remote Control Input" section, to enable use of your midi keyboard in FL Studios.
Load an instrument into the Step Sequencer, then press keys on your keyboard. You should hear notes every time a key is pressed.