Recognize the chromatic musical scale as applied to the fretboard. While this sounds complicated, it's really just the foundation of playing anything (notes or chords) on the guitar. It goes ABCDEFG and back to A again. Find out about this scale and locate each note (ABCDEFG) on the fretboard.
Find out about chords and how to play them. A chord is just a collection of notes that results in the sound of a specific chromatic note. For example, putting your fingers on the second fret of the second, third, and fourth strings lets you play an A chord by strumming all six of the strings at the same time. Learn the basic ABCDEFG chords.
Learn about major and minor. Every one of the seven chords has two versions, one is major and the other is minor. The chord described above is an A major. To make the A chord minor, take your finger one fret down on the fourth string. Play both and listen to the difference.
Experiment with fingering techniques. Fingering is the way you hold your fingers on the frets with your left hand to produce chords (unless you're left handed). You may want to follow fingering techniques laid out in books until you are confident you know how to frame guitar music yourself.
Experiment with picking/strumming techniques. When you have learned to change chords quickly, you'll probably start to experiment with picking out single notes, either with a guitar pick or with your fingers. There are many different ways to get different sounds out of the guitar. When you have graduated to this step in learning guitar, you're well on your way.