Download a professional beat-making program such as FL Studio or Sonic Producer.
Open the program and click "Track > Create New" to begin making some beats.
Select a sound, and then drag it over onto the graph. Click the empty squares along a horizontal line, filling them in to the rhythm you desire. For instance, if you chose a "kick drum" sound and you filled in a square at the beginning of each bar (divided by the vertical lines) you'll get a bass kick on the one beat. Click "Play" to preview your track as you create it.
Choose a snare drum next, filling in squares along a different horizontal line (a different track). Make sure to keep some space in between your kick drum squares and your snare squares. It's these rests that will create the beat.
Choose some high hat sounds, piano sounds, bass guitar sounds and synthesizer sounds. Repeat the process of filling in squares along different horizontal lines to get a fuller-sounding beat. Delete a square by right-clicking it if you feel it's in the wrong place. Experiment by filling in squares throughout different areas of the graph, until you achieve the sound you're looking for.
Adjust the volume of your varying sounds by selecting the track and moving the volume fader (found at the bottom of the screen) up or down, in accordance with the output level you want. For instance, if your snare drum is on Track 2, and you feel it's too loud, find the volume fader for Track 2 and move it down slowly, until you feel that the snare is at the proper volume.