Download music recording software. If you want to learn about production or get really in-depth, you can purchase a high-end production program like Pro Tools, Logic or Audition, but if you want to start with something simple or avoid spending money, you can record your rap song using a free, open-source program. Examples include Audacity, Qtractor and Ardour.
Download audio loops. To create your beat, you can use "loops," repeated audio samples (such as short drum beats or bass lines), and layer them together using your audio software. Music loops are essential to hip-hop, and websites like Looperman, Loopasonic and Free Loops have many free (and royalty-free) downloadable loops. Listen to the different samples and find ones that work with your style or mood. Read the description of each loop and try to find ones that play at the same tempo (or speed), indicated in beats per minute (BPM).
Open your digital recording software and create a new project for your rap song (File > New). Music recording programs use "tracks" for recording. Each track represents a layer (like a keyboard melody on track 1, a thick bass line on track 2 and a repetitive drum beat on track 3). To create a new track, observe the options on your menu bar (at the top of your screen). You should find a "New Track" option on one of the menus. Create as many tracks as you will need to layer your samples.
Import your loops. Some programs will allow you to drag your loops from your desktop and drop them right onto the tracks (which at this point should look like long horizontal bars on your software window). In some programs, you must select (File > Import) on the menu bar, and select the loop files using the navigation window that appears.
Drag your loops to organize them along the time line. For rap music, you will definitely want a strong percussion loop, and you may even download separate loops for different drums like kick, snare, hi-hat and cymbal. If you want two or more loops to play at the same time (like a melody loop and a bass loop), just place them directly on top of one another in their respective tracks. Organize your loops until you have the perfect arrangement for your song.
Connect a microphone to your computer. Now comes the most important part of any rap song: the vocals. You can use a vocal microphone with built-in USB connectivity for the easiest connection, or you can use a regular dynamic or condenser microphone connected to an XLR-to-USB cable (you can find all of these things at music supply stores). If using a condenser microphone (which offers the best frequency range for vocals), you will need to connect it to a USB audio interface or mixer with built-in Phantom power.
Create a new track on your software window for your vocals. Connect a pair of headphones to your computer so that you can listen to the mix while recording. For ideal quality, you should also place a pop filter in front of the mic. Pop filters look like black mesh screens, and you can find them at music supply stores. They prevent hard "P" and "B" sounds form ruining your recordings.
Put your headphones on, click "Record" on your software window and begin recording your vocals as the music plays. When you finish your rhymes, click the "Stop" button on your software window and click "Play" to listen to the finished product. If you make a mistake, you can delete the recording and try again, or you can highlight and delete portions of a recording if you only want to redo specific parts.