Many beginner guitar players are bamboozled by guitar tabs. The fact is, it's easy to understand guitar sheet music and tab as long as you remember a few basic ideas. Guitar tabs and sheet music are languages that guitar players use to show each other songs and other pieces of music.
Guitar notes are shown on tabs as numbers on lines. The lines are simply the guitar strings. The numbers are the guitar frets. The guitar tab below shows the C major chord. The top line represents the thinnest string on the guitar, so if you are holding the guitar in the playing position, the thinnest string will be near your leg. The bottom string on the tab is the thickest string which will be at the top of the guitar as you are holding it in playing position.
You probably already know that the guitar strings, from the thickest to the thinnest, sound the notes E A D G B E. The first string on the guitar is designated with a lower case e. The top e string is played open in the C chord, so there is a zero on that string. The second string, or B string, is stopped at the first fret, the G string is played open, the D string is fretted at the second fret, the A at the third, and the E string is usually not played even though it sounds the E note which is part of the C major chord.