Guitar tab or tabulature is a very popular method of notating guitar music. What makes tab so popular is that, once you get the hang of it, it is very easy to read. In order to understand tab, you need to visualize a guitar neck laying on its side like so:
At first, this will seem upside-down to you, but this view positions the neck much the same way as if you are playing the guitar and looking down on the neck. Don't worry, you'll get used to it.
Tab consistst of 6 horizontal lines that represent the strings of the guitar:
The bottom line represents the low E-string and the top line represents the high E-string. So, from the bottom line to the top line, we have low E-string, A-string, D-string, G-string, B-string and on the top, the high E-string.
In order to tell you what notes to play, numbers are used:
This tab is telling you to play the note at the 5th fret on the low E-string.
Tab is read from left to right just like you're reading these words. So if you see numbers spread out, it means to play the notes one after the other like a scale:
So, this tab is telling your to play the 5th fret on the low E-string, then the 7th fret on the low E, followed by the 4th fret on the A-string, 5th fret on the A-string etc...
If the numbers are stacked vertically, it means to play all the notes in each stack at the same time like a chord:
So this tab is telling you to play an A chord, followed by a D chord, then an E chord, and, finally, back to the A chord.
Now, notice the 0's used in each chord. 0 means to play the string without putting a finger down on it. This is called an open string.