Let's start playing guitar. Here are the first of the guitar chords you must learn in order to play the guitar. I repeat... you cannot be a guitar player without knowing how to play a G major, C major, and D major.
Look at the chord diagrams above.
The heavy horizontal line at the top represents the nut, so it's as if we're looking at an upright guitar neck. Above that line, you see that some strings are marked with a "0". This shows that the particular string is played open, with no fingers of the left hand touching it. A string marked with an "X" is not played at all, since those notes aren't part of the chord.
The other horizontal lines are the frets. The vertical lines are, of course, the strings, with the 6th (low E) string on the left.
The dots with numbers in them show (1) which string to fret, (2) which fret to play, and (3) which finger to use. We'll use this as a key: Thumb = T, Index Finger = 1, Middle Finger = 2, Ring Finger = 4, and Pinky = 5.
So, for example, in the case of a C Major chord, we use the index finger on string 2, first fret, the middle finger on string 4, 2nd fret, and the ring finger on string 5, third fret. The 6th string is not played. Easy, huh?
Practice these chords until they are second nature to you. You'll need them from now on.