Using Apple's GarageBand software, you can create your own custom rap beats by mixing and looping prerecorded audio samples. You do not need any formal music training or engineering knowledge to get started. You just need a basic idea of the type of beat you want to put together and the motivation to bring your beat to life.
Create a new GarageBand project. Click the GarageBand icon to open the file, select "File" from the menu bar and choose "New" from the drop down menu.
Select a tempo for your song. In the "New Project" window that appears, enter a tempo between 40 beats-per-minute (bpm) and 240bpm. This will depend on whether you want a fast or slow song. For a slower song, try a tempo between 80 and 110bpm. For a fast song, try a tempo between 140 and 170bpm.
Create an audio track. To do so, click the "+" button in the bottom-left corner of the GarageBand window. The screen will prompt you to choose the type of track you want, so select "Real Instrument Track" from the options provided.
Click the "Loop Browser" button to access your audio loops. It looks like a blue eye and appears directly to the right of the "+" button. After you click the button, you will see options for different types of loops in the bottom portion of your window.
Enter the words "hip hop" in the search bar directly beneath the loop browser. You will then see a list of every available hip-hop drum loop and bass loop available in your loop library.
Click each loop once to hear it and decide which loops you would like to use for your beat.
Click one of your desired loops and drag it to the beginning of your audio track using your mouse.
Repeat your loop as many times as needed. Hover your mouse over the right edge of the loop region in the track until a circular arrow appears. Then click your mouse and drag your audio region to the right. Keep moving it along the time line until you want the loop to stop.
Create a new audio track and add a second loop directly beneath your original loop. Your audio recordings will overlap for a richer custom beat. For example, you may use a drum loop for your first track and a bass loop for your second track, giving you a full drum and bass beat that you can use for your rap.
Layer additional tracks as needed. Adding too many layers will create a sonic crowding effect, but adding two or three can add complexity and depth to your beat. Explore not only the hip-hop loops, but also the other loops available in the browser.