Select the songs you want to mix. They are probably on your computer already, in mp3 format. This is the most popular digital music format and the easiest with which to work. The songs you choose to mix are up to you. Be creative and decide on the type of mixed song you want to create. Do you want the overall mix to be slow or fast? Do you want a themed mix, such as all love songs or all happy songs, or do you want an eclectic mix? The choice of songs will affect the overall feel of the mixed song and will also dictate your mixing techniques.
Find the audio software you will use to mix your song. There are several audio programs on the market (see resources). Some are expensive, some are priced reasonably, and you can even find free audio software that includes everything you need to mix your own song. Audio software allows you to cut portions of your mp3 files out to use in your mixed song. You want to look for software that includes not just the basic editing features, but special effects features as well. A good audio editing program will include features that let you fade your tracks, add echo effects, and adjust base and treble levels. The more effects you have to work with, the more interesting you can make your mixed song sound.
Open the mp3 file. Cut the portion of that song you want to use in your mix and save the file with the name you want to call your mix. Now open the next mp3 song and edit the file down to the section you want to add to the first section. Use special effects to blend the two pieces together in whatever fashion you want. You can fade the first song into the second, add an echo or mix them so they overlap. Be creative. Continue to add song pieces the same way, varying the length of each piece and the effects you use until you achieve the mix you want.
Do a final sound mix on the project when you finish adding your tracks. Adjust bass and treble levels as desired. Add any special effect you might want to add to the overall mix and save your custom mixed song.