Have you ever noticed how music is able to play over someone speaking, yet you can hear both? Whether it's in a movie, or your favorite song, sound mixing is an important part to sound design. People can forgive visual errors, but bad sound is harder to tolerate. In order to start sound mixing, here's what you need:

A computer
The free program, Audacity, which can be downloaded from its website.
Two audio samples, preferably one vocal and instrumental.
A LAME MP3 encoder, for exporting MP3 projects.(When you try to export, it should plug in by itself.

In addition, make sure you save your work. Audacity can have issues with crashing.

Step 1: Install and Open Audacity

Upon downloading the program, open it. This is what the application looks like.

Step 2: Import Audio Into Audacity

Go to File > Import > Audio and bring in the two audio sources you want to use. The resulting files should look like this.

Step 3: Experiment With Volume

Use the scales on the left of the songs, or Effect > Amplify to play with volume. Make the vocals louder than the music. Or, you can use Effect > Audio Duct, but it isn't as efficient as manually fixing audio. This way, you can tell when the music begins to spike up in sound, which leads to the next step...

Step 4: Normalizing Your Audio

Normalizing the audio means balancing it in a way none of the audio gets too loud or quiet at an unexpected rate.

You can use Effect > Normalize, but I find it easier to manually highlight, and play with amplification via the Effects panel. This is to prevent unnatural spikes in your sound, and make it easier to control volume on an entire clip

Step 5: Regulate Bass and Treble Settings

In the Effects tab, you'll see an option for bass and treble. Treble makes voices stand out, and bass increases vibrato in sound, mainly instruments. Use very little treble on the voice to make it stand out, and lower treble (not by much!!!) and add a little bass to the vocals. This varies on the audio tracks, and experimentation may vary.

Step 6: Export Your Audio

After getting the sound to balance in a way that's comfortable, it's time to export. Go to File > Export > Export as [desired audio format]. Upon doing this, your file will finish and be loaded.