Unless you are using an electronic tuner, to be able to tune the guitar accurately by ear usually requires many months of practice. You will probably need your music teacher or a musician friend to help you tune when you are learning.
Outlined next are the methods for tuning to concert pitch. This is a standard tuning that all musicians tune to so that they can play "in concert" with each other. It is possible for a guitar to be in tune with itself (e.g., you strum a chord and it sounds in tune) but out of tune with a piano which would be tuned to concert pitch. Also explained is a method of tuning the guitar to itself. This tuning method is essential to know because when tuning to concert pitch you may only be given one note (usually the open 5th string A) so you have to know how to tune the other strings to this note.
See Electronic Tuner in the Introduction.
Another way to tune your guitar is by ear to another guitar that is already in tune. You can do this by tuning each string of your guitar to the same string of the other guitar.
The first note tuned is the open 6th string (E note):
Now follow this procedure for the other strings. To check if your guitar is in tune strum a chord.
If you are playing along with another instrument, it is essential that your guitar be in tune with that instrument. Tune the open strings of your guitar to the corresponding notes of the accompanying instrument.
To tune to a piano, tune the open 6th string to the E note on the piano, as shown in the next diagram. Then tune your guitar to itself from this note, using the method outlined below, or tune each string of your guitar to those notes of the piano shown on the diagram.
A tuning fork produces a note (usually the 5th string A Note) which you tune one string to. Then you tune the other strings to that string, using the method outlined below.
Pitch pipes produce notes that correspond to each of the six open strings. Tune each string of your guitar to each of these notes in turn.
If you do not have another instrument to tune to, you can tune the guitar to itself by using the following method:
One of the easiest ways to practice tuning is to actually start with the guitar in tune and then detune one string. When you do this, always take the string down in pitch (i.e., loosen it) as it is easier to tune "up" to a given note rather than "down" to it. As an example slightly detune the 4th string (D). If you play a chord now, the guitar will sound out of tune, even though only one string has been altered (so remember that if your guitar is out of tune it may only be one string at fault).
Following the correct method described earlier, you must tune the open 4th string against the D note at the fifth fret of the 5th string. Play the note loudly, and listen carefully to the sound produced. This will help you retain the correct pitch in your mind when tuning the next string. Now that you have listened carefully to the note that you want, the D string must be tuned to it. Play the D string, and turn its tuning key at the same time, and you will hear the pitch of the string change (it will become higher as the tuning key tightens the string). It is important to follow this procedure, so that you hear the sound of the string at all times, as it tightens.
You should also constantly refer back to the correct sound that is required (i.e., the D note on the fifth fret of the 5th string). You will hear a wavering sound created when the 2 strings are played together. This wavering will gradually slow down as you come back into tune and then become still when the 2 strings are in tune.