Go to an online beat generator, such as JamStudio.com. These sites allow you to create chord, instrumental, bass and rhythm elements.
Select the chords for your score from the box labeled "Chords" that lists keys; the chords determine the melody of your beat. You have to select a chord for each bar and measure of the score. The score automatically populates as you choose the chords.
Choose the instruments you would like from the box labeled "Mixer." Hit the play button to preview the sounds of each instrument. To create only beats, rather than harmony or melody, you should only select from drum and rhythm instruments.
Set the volume and the tempo of your beat by sliding the volume, to the right of the instrument name, and tempo sliders, on the left of the Mixer box.
Denote the music genre and sub genre for your beat from the box labeled "Sounds," which simply denotes the style of your instrument, such as "Snare Drum."