Open Cubase SX 3 and create a project for your beat. Click the "File" menu at the top of your screen and select "New," and a new blank project window will appear on your screen.
Connect your instrumentation, if applicable. You can create beats in one of two ways: using your own instrumentation or using pre-recorded loops (samples), which you can layer to create original sounds. If using your own instruments connected via USB, first plug the device(s) into your USB port(s), then click the "Device" menu at the top of your screen, followed by "Device Setup" and then "VST Audiobay." Select your connected instruments from the list of possible inputs.
Create an audio track by clicking the "Project" menu and selecting (Add Track > Audio). Press the "Record" button on your project window and begin playing your instrument to record an original bass line, melody, drum sample or other instrument. If using loops instead of original instrumentation, click the "File" menu and select (Import > Audio File). Use the navigation window to select a loop from your hard drive. You can download thousands of loops for free on the Internet (see “Resources”).
Create a second track for your second layer of music. For example, if you recorded a bass line or imported a bass loop onto your first track, then you might follow up with a percussion piece on your second track. Add as many layers as you need for your particular beat.
Mix your music. To add an effect (such as reverb) to a track, select it with your mouse, click the "Inserts" button on the left side of the screen and select an effect from the menu. To adjust the EQ (equalization) of a given track, select it with your mouse and click "Equalizers" on the left side of your screen. Use the grid to adjust your high, middle and low frequencies and obtain just the right balance for your sound.
Click (File > Export > Audio Mixdown) to save your beat as an audio file that you can transfer to an MP3 player or send to your friends. Enter a name for your beat, choose your desired audio format and click "Save."