Plan your composition before you begin recording. Identify each sound you want to record and assign it to its own track. For example, you might have three tracks -- music from a guitar, drums from a synthesizer and voice. Choose the sound that will best carry the melody of the song for the first track because it will serve as the basis for recording the other tracks. For example, you might record guitar music first.
Download and install a free digital audio editor. Plug the microphone into the microphone jack on the computer, press "record" in the digital audio editor and test the recording volume of what will be on the first track. Adjust the volume so that the meter stays out of the red area to avoid distortion, also known as "clipping." Delete the audio track when you are satisfied with the levels.
Press the "record" button and record the first track. Play the piece from start to finish. While it's possible to edit out mistakes, at first it's best to start over if you make a mistake and try to record a track that you'll be satisfied with as is.
Export the first track to an "mp3" file format. Open the exported file with a built-in media player such as Windows Media Player. In the digital audio editor, prepare to record the second track by experimenting with the audio levels until they stay out of the red range. Plug your headphones into the headphone jack, press "record" in the digital audio editor and "play" in the media player. Record your second track over the microphone as you listen to the first track through the headphones. Repeat the same steps for the remaining tracks in the composition.
Use the features in the digital audio editor to mix your tracks together. You may need to edit out lead-in silence and line up the tracks so they play in sync with one another. You'll also want to adjust the volume of each track individually so they blend together to create the sound you want. Begin editing with the first two tracks; use the "mute" or "solo" buttons to isolate them. Add the other tracks one at a time until you have mixed them all together.
Experiment with the many effects in the digital audio editor such as the Equalizer and the Compressor to fine-tune your mixed composition. Export it to an "mp3" file format when you're done. If you mixed the tracks using headphones, play the composition over speakers to make sure the sound is as you expect it to be.