Acquire a digital audio workstation. A digital audio workstation is software that is capable of mixing or making music. If you have multiple tracks of a single song saved as separate WAV files, then make sure the digital audio workstation is capable of opening MP3s or WAVs.
Load a track into your digital audio workstation. In most digital audio workstations, you can click "File" from the toolbar and click "Open." From here, browse to the location of your track. Most, if not all, digital audio workstations will allow you to open multiple tracks of a single song at the same time.
Use a graphic equalizer to cut out certain frequencies. Most digital audio workstations have a sidebar with a list of available devices. Find the graphic equalizer and drag it into a track. Keep in mind what instrument you are mixing for. If you are mixing a bass, boost the low frequencies to emphasize the bass. Make sure it will sit well with the other tracks. Use your ears to determine whether or not to boost frequencies that are too weak or cut frequencies that are too overpowering.
Use the mixer to change volumes of certain tracks. The mixer is usually located alongside its respective track. Drag the slider up to increase volume and down to decrease volume. If your volume is too high, a small box above the volume bar will turn red. This means that your track is "clipping." Make sure your track does not clip, as this will sound undesirable, especially at high volumes.
Change the panning of tracks in order to create space in your mix. Panning refers to how much of a track is played through the left and right speakers. If two tracks have clashing frequencies, a common technique is to have one track play from the left speaker and the other track play from the right. To pan a track, go to the mixer window of your digital audio workstation. Near the volume faders, there is usually a knob that has "L" on the left side and "R" on the right side. Drag the knob to the left to pan the entire track to the left. Drag the knob to the right to pan the entire track to the right.