How To play Guitar Lesson By Lesson----> lesson 3

Lesson 3: Tuning Your Guitar
For beginning guitar players, it is often a good idea to purchase an electronic tuner. Electronic tuners are small devices that are able to pick up the sound of a string and let you know (usually through some sort of L.E.D. display) whether the note you are playing is sharp (too high) or flat (too low). Since beginners usually have a hard time telling whether or not a string is in tune just by ear, having an electronic tuner can help make tuning much quicker and more accurate. For more information, see Mahalo's guide to Guitar Tuners.
For those that don't want (or can't afford) to purchase an electronic tuner, there are other ways to tune your guitar manually and without the aid of an electronic device. The simplest way is to use a method called Relative Tuning:
Relative Tuning
Place a finger on the 5th fret of the 6th string and play the note.
Play the 5th string "Open." When in tune, these two notes should sound exactly the same.
Adjust the tuning peg for the 5th string so that, when played open, it makes the same sound as the 5th fretted 6th string.
Place your finger on the 5th fret of the 5th string and repeat this process with the 4th string "Open."
Repeat this process for the 4th and 3rd strings.
When you reach the 2nd string, things change slightly. Instead of placing your finger on the 5th fret of the 3rd string when adjusting the 2nd string, place it on the 4th fret.
To tune the 1st and final string, go back to the previous method by playing the 5th fret of the 2nd string.