Start a new audio project in GarageBand. Open the program by clicking on the guitar icon in your "Applications" menu, or in the dock along the bottom of the screen. Click on "File" and select "New" in the drop-down menu. Name the project, and set the song's tempo. Techno songs generally are 120 to 170 beats per minute. Then click the "Create" button to continue.
Click the "+" button near the lower-left corner of the screen. This opens a window that allows you to create a new audio track. The first track will serve as the first musical layer of your song, and should be used for drum loops. Select the "Real Instrument" option for the track, and click the "Create" button. Name the track "Drums."
Click on the "Drums" track to enable it for recording. Select the "Browse" tab on the right side of the window. Click on the "Drums" menu, then click on each drum loop sample in the menu to hear it. Once you have located the desired drum loop, drag and drop it into the "Drums" track.
Click on the "+" button again. Select the "Real Instrument" option, and click on the "Create" button. Name the track "Bass." Repeat this to create an additional track. Name the real instrument track "Synth."
Select the "Bass" track to enable it. Click on the "Bass" menu in the "Browse" menu in the right panel of the GarageBand window. Again, click on each bass loop until you find the desired loop. Drag and drop the loop into the "Bass" track window. Drag the bass loop until it is perfectly aligned with the drum loop in the first channel's window. Repeat this to select a synthesizer loop for the "Synth" channel.
Press the play button in the playback transport near the bottom of the screen. Mix the tracks to your desired audio levels. This involves raising and lowering the volume button on each individual track until they blend together to your liking. In techno songs, the bass line and drums are generally more prominent in the mix, while the synth line is a little lower -- to provide a melody for the song.
Click on the "Master Track" tab in the right panel of the window. Select the "Track Info" column, and click on the "Dance" option. This gives the track a low-end and bass-heavy mix that is common in techno recordings.
Go to "File" and click on the "Save" button in the drop-down menu. This saves all changes made to the project file.