Grab the guitar and put it comfortably on your knee, or sling the strap around your back. Pick up a guitar pick, or get your finger ready to pluck the E string, or top string of the guitar.
Play your MP3 E note and the top string--the E string--at the same time. If the guitar is out of tune you will hear dissonance or a sound that does not seem right. If the E string on the guitar sounds lower than the MP3 E note use the tuning peg to tighten the E string. If the E string on the guitar sounds higher than the MP3 E note use the tuning peg to loosen the E string.
Tighten or loosen the E string on the guitar until the MP3 E note and E string make the same sound. You will know the strings sound the same when the dissonance goes away. The location of the strings to the tuning pegs will vary depending on the guitar so just follow the string you are tuning to the head of the guitar to see which peg to turn.
Hold down the string on the fifth fret on the E string, and pluck the open A string, the second string from the top. There are small bars of metal running up the neck, separating the neck into sections called frets. Tighten or loosen the A string until it is in tune with the fifth fret of the E string. Repeat this process for the D string and the G string (the third and fourth strings from the top).
Hold down the fourth fret on the G string and tighten or loosen the B string (the fifth string from the top) until it is in tune with the fourth fret of the G string.
Hold down the fifth fret on the B string and tighten or loosen the high E string (the sixth string from the top) until it is in tune with the fifth fret on the B string.