Download the right software. You can choose from many free digital audio workstations designed for Windows, Mac OS X and Linux. Check out free recording programs like QTractor, Audacity, Ardour and Traverso DAW. Look at the system requirements and download a suitable program.
Record your music, if necessary. If you want to mix music of your own, record it using your free software. Open the program, create a new song file by selecting "File" then "New" and begin recording. The "Record" button usually appears as a red circle, although some programs may indicate the button with a letter "R" or the word "Record."
Separate your recording into layers. To record your song one layer at a time (for optimal mixing), locate the "Create Track" or "New Track" selection on your menu bar and create a separate track for each instrument or voice. Each track will look like a horizontal strip or bar across your screen. Select any track and begin recording one instrument or voice. For instance, you might select "Track 1" on your screen and record a guitar melody, then select "Track 2" and record a bass line while the previously recorded guitar melody plays.
Import music. If you want to mix an already recorded song file, drag it onto your software window or add it to your project using the "Import" option (usually appearing beneath the "File" menu at the top of your screen). You can find free and legal music samples at websites like Looperman, Loopasonic and Free Loops. If you want to mix multiple samples together, just place each loop on a different track with your mouse.
Mix your tracks. If you chose to arrange several tracks rather than one self-contained song file, you can mix your layers precisely using the track options, some of which should appear in the left column of each track bar. For instance, if you see a knob or slider that reads "Level" or "Volume," use it to raise or decrease the volume of each track until all of your tracks sound balanced. Next to the "Level" indicator, you should find a "Pan" dial, which you can use to move different instruments to the left or right. Locate your "Effects" menu (sometimes on the menu bar, sometimes on the project window) to apply digital effects to individual tracks.
Mix the overall song file. If you have only one self-contained file (rather than individual tracks), you can still adjust individual parameters by opening your "EQ" window, found on the "Effects" menu, or found on the menu bar. A standard EQ may consist of a grid or a slider. You will see "Low," "Mid" and "Hi" frequencies, or you will see "Bass," "Mid" and "Treble" frequencies. They may also appear numeric (low to high frequencies always appears from left to right on a grid). Adjust these frequencies on your grid to mute excess bass or add brightness to a flat mix. Remember that low frequencies correspond to low sounds, and high frequencies correspond to high sounds. Adjust your mix accordingly.