Get something that makes beats. A drum machine or beat-making program are inexpensive ways to create beats at home. Lacking either, find a friend who can beatbox.
Lay down a basic beat on your beat-making device. Most beats consist minimally of a bass drum and a treble beat. Your drum source may have built-in beats that can help you get started. If you don't want to make your own beat, find a musician who will let you use her beats.
Freestyle rap over your beat. When freestyle rapping, think of lyrical rhythms that you have heard from artists that you admire. Try to use your own words with rhythms similar to those performed by your favorite rappers. Keep the beat playing while you write. When you write something that might make a good hook or chorus, mark it so you can come back to it later.
Practice delivering the written lyrics smoothly to ensure fewer mistakes during recording.
Download and install an audio-editing program on your computer. Audacity is a popular, free audio editing program that you can download.
Plug a microphone into the microphone jack in your computer. From the "Edit" menu, go to "Preferences," then "Devices" to set your computer to recognize the recording input from your sound card.
Import your beat into the program by accessing the "Import" function in the "File" menu.
Hit the record button to commence recording. Perform your rap lyrics for the recording program to the beat you imported. Press stop when you are done. Save your track by selecting "Save" from the "File" menu.
Make the track a listenable audio file by selecting the "Export" option in the file menu. Choose a file type that will work for your purposes. Popular file type mp3 is a small file that can be read by most players, but it is a compressed format that loses some audio quality.