the basic chord structure for thesong is G, B, C, Cm. This changes on
every line so the bass tab is simply to when the chord changes you go
to the relevant fret on your bass.
When the chord changesto G the bass is on the 3rd fret on the e string,
for B it is on the 7th fret of the E string, the 8th fret on the E
string for the c and for the Cm it is on the 3rd fret of the A string.