The first step is to understand what we are going to do here. We're not learning how to read music, compose our own songs or become musical geniuses. We are simply going to learn a method whereby we can pick up a guitar and learn or play a song of our choosing.
First we must understand the strings and frets of a guitar. The strings of a guitar are numbered one through six from skinniest to fattest string, or from bottom to top as the guitar is held in playing position. Remember, small string, small number. In this picture, the strings are numbered one through six from right to left.
The fretboard is on the neck of the guitar. The frets are numbered from the top down when the guitar is in an upright position. Fret one is at the top, then fret two beneath, then fret three, etc.
Find a playing position that is comfortable. At first, the guitar will feel big, bulky and unwieldy. That's okay. the more you handle it and play it, the more comfortable you will get with it. Many people own many types and sizes of guitars, and as a result, they have many types of playing positions. Some sit, some stand, some use a guitar strap, some use a foot stool. Find what feels best for you, as your playing position will affect your playing ability.
It's now time to read tablature. Guitar tablature is kind of like a cheat sheet. It looks similar to standard musical notation, but, in reality, does not work the same at all. The major visible difference between standard notation and tablature is that standard notation has five horizontal lines, while guitar tablature has six lines. In tablature, the six lines actually represent the strings of the guitar.
If the guitar were held in a standard playing position with the neck horizontal to the floor, then flipped over so that it were facing the player, the strings in this position would exactly represent how the lines of tablature are written. In other words, the top line of the tablature is string one and the bottom line is string six.
The numbers on the tablature represent which fret each string is to be be played on. For instance, in this tablature, the first note would be played on string four, fret four. The second set of notes would be played on strings four and five at frets five and three respectively. In the third set of notes string two would be played open or unfretted while string four remained fretted at five, and the fourth set of notes would have the first, second and third strings fretted at two, three and two respectively.
No, this is not easy. If it were, the guitar would not be considered one of the most difficult instruments to play well. But, with diligence and perseverance and lots and lots of practice, this method can be learned very quickly.
Tablature is readily available all over the internet. Literally just about every song that can be played on guitar has been tabbed by someone. Below, I've listed some links to popular tablature sites.