Learn guitar tablature. Guitar tablature is the form of musical notation specific to the guitar that indicates instrument fingering in written form. Learning guitar tablature ("tab" for short) is akin to learning the alphabet in order to read. Tab consists of six horizontal lines that represent the strings of the guitar. The bottom line is the low E-string and the top line is the high E-string, with the other strings B, G, D, and A in between. Numbers indicate frets and tab is read from left to right. Zentao has a helpful tutorial online for tablature.
Learn to play basic chords. Chords are the basic structure for all music. Guitar chords are created by placing the fingers along the neck of the guitar on particular strings at particular frets. Each guitar has frets along the neck. These are metal strips that act as guides to create chords. Use video tutorials online to master the placement of fingers on the guitar frets, or for some of the basic guitar chords, including A, E and D. A viritual chordbook online provides demos of the placement of fingers for basic and advanced guitar chords.
Learn how to strum. Strumming is what gives guitar playing its rhythm and various strumming techniques create distinct musical effects. There are video tutorials online that teach strumming techniques, with instruction in how to read and play rhythms. For example, the rhythmguitarzero2hero basic strumming video tutorial teaches about down strokes and up strokes, rhythm slashes, repeat signs, and quarter and eighth notes.
Learn finger-picking techniques. There are several styles of finger picking: classical, country and pop style. You can learn all these styles or just the one(s) you prefer, but each requires a basic introduction to finger picking. The rhythmguitarzero2hero tutorial, for example, teaches the written notation for each finger (Left hand: Th, 1, 2, 3 and 4 and right hand: P, I, M, A, C) so you can read finger-picking notation. You will also learn some of the general rules for finger-picking and some basic patterns.