Open online chromatic tuner . Your browser should support Flash. If you use good microphone or if you connect your guitar to the “line in” input, you’ll increase accuracy of tuning.
The strings of a guitar from the thickest to thinnest:
1 (E) 329.63 Hz E4 the thinnest or highest is the 1st
2 (B) 246.94 Hz B3
3 (G) 196.00 Hz G3
4 (D) 146.83 Hz D3
5 (A) 110.00 Hz A2
6 (E) 82.41 Hz E2 the thickest or the lowest(6th string)
The thickest string(6th String) note is E. You can find it on a picture.
Put the guitar in close to the microphone(notebook) and play the first note (low E).
If your string tunned correctly you’ll see note “E” on the screen and accuracy near “0”(center of the bottom scale) and scale will glow with green color.
If tuner application showing you wrong note or big deviation( light is red and not at the center of scale)you should turn the tuning knobs on your guitar and match them up with the note showing by the online tuner. So guitar tuner shows proximity of the playing note at the bottom. You can also check accuracy by color. If scale has green color than current string where tuned correctly.
Then repeat this procedure with other strings.