Purchase a music-editing program, such as Reason, Pro Tools, Logic, Ableton, Cubase, Sibelious, Garage Band, Fruity Loops or Sonar. Research these programs carefully before buying, as different programs are higher or lower in quality, some are cheaper or more expensive and some have audio, or live recording, abilities, while others have MIDI, or sample, recording abilities. Most programs have MIDI abilities, but you will need the audio component if you wish to sing or play real instruments.
Install the program to your computer; connect the MIDI device, such as a keyboard; and configure your particular program to accept signals from MIDI controllers. MIDI controllers allow you to simulate with your fingers in real time what you want the computer play. For example, if you are recording and hold the C key for three seconds, the computer will record three seconds of any chosen instrument, such as a guitar or violin, playing a C. This makes recording quick and easy. Without a MIDI controller, you must manually draw, or place, notes when, where and how long you want them played.
Create an entire instrumental using MIDI if desired. The better the quality of your program and plug-ins, or samples of instruments and effects, the more realistic your song will sound.
Purchase basic studio equipment if you wish to involve real instruments. You do not need as much as real-home studios, especially if you only wish to add vocals or a single instrument, such as an acoustic guitar. Buy an audio interface, which already comes with some software programs; a microphone, if recording vocals or non-direct instruments; and any cables to connect your equipment.
Use your plug-ins and effects, such as reverb, delay, compression and equalization, to perfect the sound of each instrument as well as the overall song. This is done in both audio and MIDI recording.
Export your song from the program and upload it to the Internet or load it into your MP3 or other music player to begin sharing it with friends. Once you become good at recording, try to sell your instrumentals.