Download a free digital audio program, such as Ardour or Traverso. You can find many free and open source audio editors online, but make sure to download one that has multi-tracking capabilities.
Download free audio loops. Audio loops are short sounds, such as drum beats, melody lines and sound effects that you can layer to create original beats for your own use. A variety of sites, such as Looperman, Free Loops and Sample Swap, offer free professional loops for personal and commercial use. Download a variety of percussion and melody loops that sound good to you, and notice the tempo (speed) beside each loop, indicated by beats per minute. Try to download multiple loops with the same tempo, so that you can layer them together without having to contend with multiple contradictory speeds.
Open your digital audio program and create a new project. You should see your blank audio tracks arranged on top of one another as long horizontal bars across the screen, labeled with names like "Track 1" or "Audio Track 2."
Choose a drum or percussion loop and drag the file onto a blank audio track. Just use your mouse to drop the file at the beginning of the track, on the left side of the window, and repeat the loop as many times as needed by clicking and dragging the right edge across the time line.
Choose a melody or instrument loop and drop it onto a blank track directly beneath your percussion track, also at the beginning of the time line. You now have overlapping rhythm and percussion.
Choose a sound effects loop or an additional percussion loop and place it onto its own track directly beneath your melody track. This will add dimension and complexity to your beat, making it even more professional and original.
Add additional loops to your beat in the same manner as needed. In most cases, you should not need more than four or five loops for a single beat, as adding excess loops can create a sonic crowding effect that takes away from the professionalism of your sound.
Save your work.