Download a free audio mixing program. A simple audio recording program will not suffice. In order to mix professionally, you will need a program that allows multi-tracking. Try a free multi-tracking program such as Audacity, Ardour, QTractor or Traverso.
Find music to mix. Sites such as Shockwave Sound, Looperman and Loopasonic contain libraries of royalty-free audio and music samples that you can edit, layer or mix together. In addition, you can find free and legal music online from the nonprofit Archive.org, The Library of Congress, and websites such as Project Gutenberg and Incompetech.
Open your audio mixing program. Sometimes you can import audio files simply by dragging them onto the program's main window. In other cases, you will need to select the "Import" option from your menu bar (typically found beneath the "File" menu). Import a song file into your mixing program, or input a series of samples that you want to mix together.
Arrange your sound files. If you imported a single song file, it should appear as a horizontal bar consisting of wavy lines (your audio wave forms). If you imported multiple files and samples, they should appear on individual tracks (several horizontal bars stacked on top of one another). If they do not appear on individual tracks, separate them by clicking the "New Track" or "New Audio Track" option on your menu bar or tool bar. Create one track for each sample, and use your mouse to drag the tracks so that each appears on its own track.
Add effects. Each mixing program has an effects menu, sometimes accessed from the menu bar (via an "Effects" or "Plug-Ins" menu), sometimes from a digital mixer window, and sometimes from an effects window. To add an effect, first select the track that should receive the effect. For example, if you want to add a distortion effect to a guitar track, select the track containing your guitar sample. Then choose an effect from the menu to apply it directly to the track. You can also apply effects to complete song files.
Balance your tracks. Each track has its own volume indicator, usually appearing as a round knob or vertical slider. Adjust the volume on each track so that the different parts of the mix blend appropriately. No track should dominate the entire mix. Your tracks should also have a knob or horizontal slider that reads "Pan." Use this to move individual sounds to the left or the right, creating a surround sound effect.
Equalize your tracks or your main mix. Along with your effects, you should find an option that reads "EQ" or "Equalization." An EQ grid contains three types of sounds: bass (low), mid-tones and treble (high). Sometimes these frequencies are divided over several numeric figures, moving from left to right (low to high). Use the grid to adjust your frequencies and improve your mix. For example, raising the low frequencies will create more of a bass presence, and raising the high frequencies can make a mix sound brighter.