The very top string on your acoustic guitar should be the note of E. Listen by ear to the note you find in the References section, or to the note you find on your tuner, and tune the top string until it sounds exactly the same. Listen carefully to get this note right -- all of the rest of your tuning will be based on it.
Tune your second string down to the note of A. If you place your finger on the fifth fret of the top string and hold it down, this will give you the sound of A. Listen by ear and tune the second string to the exact sound you hear.
The next string down needs to be the note of D. Follow the same process as Step 2, only a string further down; simply place your index finger on the fifth fret of the A string and hold it down. Take the sound you hear and tune the third string from the top to this note.
The fourth string from the top is called the G string. The G note can be formed by taking your index finger and holding the fifth fret of the D string down. Tune the fourth string until it is the same as this note.
The fifth string down is called the B string. The sound of the B string is the same as holding down the fourth fret of the G string. Just copy the sound until the fifth string sound is the same.
The sixth sting down is called the E string. There is a difference from the first E we talked about earlier. The first E is also known as the Low E. The second E is known as the high E. The strings are one octave apart. Tune this string by holding down the fifth fret on the fifth string -- the open sixth string should hit the same note.