Learn the names of the open strings, or the notes for each string if you aren't holding down a fret. The guitar is made up of six strings, with the thickest, heaviest string at the top and the thinnest string on the bottom.
Guitar strings count from the bottom to top, so the thinnest string is the first and the thickest string is the sixth. From the bottom up, the notes are E-B-G-D-A-E.
There are a variety of ways to remember the strings, but one of the simplest is:
Memorize this simple rhyme and you'll be playing in no time.