Choose your midi controller. Commonly, midi controllers are found in keyboards, professional audio software, and foot controllers. What makes something a midi controller is its ability to send midi signals through built-in midi connections. These controllers will not always have their own built-in sounds, but will rely instead on midi to trigger sounds from a midi-controllable instrument.
Choose a midi instrument that you would like to control. Most commonly, a midi instrument will be a rack-mounted synthesizer. These instruments take the incoming midi notes and recognize them as musical note values. The synthesizer then reproduces the note using its own built-in tones.
Connect your midi cable to the midi-out connection on the back of your controller.
Connect the other end of your midi cable to the midi-in connection on your instrument. The midi signal will now flow from the controller to the instrument allowing you to control the instrument's built-in sounds.