Begin a new project in your Digital Audio Workstation.
Create a new MIDI track for each voice in your arrangement. On most DAW programs, a new MIDI track can be created either through accessing a drop-down menu or by right-clicking in the project window.
Assign a virtual instrument to each MIDI track. Many virtual instruments are synthesizers or are created by synthesizers. Your DAW will either have onboard synthesizers or allow for the use of synthesizer plugins, which are external programs that can be imported into your project.
Connect your MIDI controller to your computer's USB port if you wish to play the melodies for your MIDI tracks. Make sure your MIDI controller is selected as the input device for the desired track.
Click on the record-enable button for the track you will record first. The record-enable button looks like a small record icon or an "R". This ensures that the MIDI messages sent to your computer are written only to the desired track(s).
Press "Record" on the DAW transport; the transport is the panel with global Stop, Play, and Record buttons.
Record the MIDI notes for the desired track by playing your MIDI controller or your computer keyboard. You may also manually draw notes into the track by using your mouse.
Press "Stop" on the transport when you have finished recording.
Record for every other MIDI track separately.
Edit an individual track's melody as necessary. While composing a song, it may be useful to revise parts of a melody as you add more tracks.