Each line represents a string on the guitar. The bottom line on a tab correlates to the low E string and the top line refers to the high E string, with every line in-between correlating to the strings in-between on a real guitar. It's easier to picture the tab as if you were looking down at your guitar while it's sitting in your lap, so it would read EADGBE (low to high). Now, the numbers on the tab refers to what fret you're supposed to apply pressure to. For instance, consider this:
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--------4---------
--------4---------
--------2---------
That tab would mean to have a finger on the 4th fret on the D string, a finger on the 4th fret on the A string, and a finger on the 2nd fret on the low E string.
If you need more explanation on what other tab symbols mean, look at this article
http://www.ultimate-guitar.com/lessons/for_beginners/reading_guitar_tablature_ii.html