Guitar/Understanding the Strings

To properly understand the strings, the guitar must be in tune. The strings should be tuned to EADGBE. That is, the thickest string should be a low E, the next an A, and so on. This is called standard tuning. Other tunings exist, but we should not concern ourselves with them yet.

The fifth (standard A) and fourth (standard D) strings
The fifth string behaves similarly to the others: each fret is a single semitone up from the previous fret. The fifth fret on the fifth string is a D, which is the same note as the open fourth string. Likewise, the fifth fret on the fourth string is a G, the same as the open third string. This is the fret used to tune the string above it.

The third string
This string is slightly different from every other string on the guitar. The reason is the fourth fret on this string, not the fifth, has the same note as the second string.

The second string
The fifth fret is an E and the same as the open first string.