To use a reference mix, simply import the song into your DAW, on a new track. Make sure you don't have any compressors or mastering plug-ins on the master fader because they will interfere with your imported track. Lastly, make sure that the song is level matched against yours. That is, your reference needs to be at the same level as your mix.

Use a Proper Reference

Make sure from the start that you're actually using a good reference mix. If you think your mix is bad, it won't do you any good to compare it to another sh*tty sounding song.