Reading tab is very easy. The only problem is, it generally doesn't give you any sense of the rhythm of the song (some very very good ones can though), so you have to listen to the song as you learn it. Generally:
e----
B----
G----
D----
A----
E----
represent the six strings. Of course, the low E is at the bottom, and then A, D... etc etc. Any numbers written in the same column mean that those strings are played at the same time. Numbers along the rows indicate notes played on those strings. The different numbers refer to the different frets. eg:
e----4
B----
G----
D----
A----
E----
Means you play the high e string at the 4th fret.
e----
B----
G----
D----
A----3
E----1
means you play both the 1st fret of the low E string and the 3rd fret of the A string at the same time.
e-------
B-------
G-------
D-------
A------3
E----1--
means you play the 1st fret of the low E string first, and then you play the 3rd fret of the A string next. Chords can be written in tab very easily as well:
e----0
B----0
G----1
D----2
A----2
E----0
Is your standard Emaj chord...
Some more advanced notation is as follows:
---/3--- usually means slide up to the 3rd fret. ie, hit the string as your finger slides up to the 3rd fret.
---2/3--- usually means slide from the second fret to the 3rd... ie, play the 2nd fret, then slide to the 3rd.
---2h4--- usually means "hammer on". Play the 2nd fret, with say, your index finger, and then put your middle finger down on the 4th fret without plucking the string again.
---4p2--- is the opposite of "hammer on". It's called a "pull off". Play on 4, and pull off to your finger already pushing down on 2.
--2^3-- refers to playing a note on the 2nd fret and then bending the string up to sound like the 3rd fret.
---12h--- can mean play a harmonic above the 12th fret (if you don't know what harmonics are, don't worry about it right now)
---12th--- can mean playing a tap harmonic at the 12th fret...
---8ph--- can mean play a pinch harmonic at the 8th fret (these sound frickin awesome if you've got an electric with some reverb and distortion)
Oh, and --4~~~~~--- usually means play a vibrato at the 4th fret... (again, don't worry if you don't know...)