Place two song files on to your computer's hard drive. Use a program, such as WinAmp, Windows Media Player or iTunes, to rip the tracks if you need to copy them from a CD.
Install a multi-tracking program. In order to mix one song into another, you "layer" the two songs by placing the files on top of one another. You can achieve this using a multi-tracking program, also known as a DAW, such as GarageBand, ACID, Cubase, Reason, Audition or a free program, such as Audacity, Qtractor or Ardour.
Open your multi-tracking program, and import your first song file. You may drag the song file image from your hard drive directly onto the software window. Other programs require you to select the "Import" option, found under the "File" menu at the top of your screen. Multi-tracking layouts involve long horizontal bars that represent your layers, or individual files stacked on top of one another, so your song file spans across your screen between two horizontal lines, usually indicated by wavy lines, the animated wave forms of your audio file.
Import your second song file. It appears directly beneath the first, on a separate horizontal bar. Press "Play" to hear both songs play simultaneously. Begin editing your song files.
Delete the sections of each song that you want to omit for your new music mix. For example, if you want to keep the first song in tact but use only the chorus of the second song, delete all parts of the second song except for the chorus. Highlight the unwanted portions of either song with your mouse, and press "Delete." Some programs include a "Cut" or "Split" option, which allows you to click the "Start" and "End" points of the unwanted regions and delete the space in between.
Rearrange the portions that you want to keep. To move parts of a song around, drag any remaining region along the time line that appears at the top of your screen, while remaining inside the horizontal track space. Apply effects to each track by making selections on your "Effects" or "Track Editor" browser.
Fade one song into another using the "Fade In" and "Fade Out" options. To create a DJ mix by fading the end of one song into the beginning of another, apply a "Fade Out" effect to the last five to 10 seconds of the first song, and apply a "Fade In" effect to the first five or 10 seconds of the next song. These options are under your program's "Track Automation" or volume editing options. You may need to manually draw the fading effect on a horizontal volume grid by drawing an upward horizontal slope, fade in, or downward horizontal slope, fade out. Make sure to overlap the song files within their respective tracks by about 10 seconds on the time line.