Tabs are basically a series of lines that represent the strings of your instrument.
On those strings are numbers and those numbers represent the fret that you're supposed to play on that string.
Like the following:
G----------------------------0--
D-----------------0--2--4-----
A-----0--2--3-----------------
E--3----------------------------
Would be the G major scale on a 4 string bass starting on the 3rd fret, low E string and ending on the open G string.
Tabs can be helpful in explaining some things but don't expect them to tell you exactly how you should play something and what kind of feel you're to express.
For the most part tabs can be very crude and should only be used to compliment using real charts, real theory, and your ear.
