Whats the relation between Tabs and Chords

yaa their is a relation B/W chords and bass, for any chord their are its relative bass notes, you can play these bass note for that particular chord.
example:- for G chord u can play G note on e string on bass or open d string
or even B. And u will see that all these notes together form G chord, so u can only play bass notes relative to their chord , other wise it will not sound good.

And u have these bass notes played along chord in same guitar on in bass guitar seperatly.

u might have seen thing like D/A or A/E or C/B in chord progression
it means for D chord A note is played in its background as bass
for Chord A , notes E is played in its bass
and last for C chord B is played as bass