All you have to do is listen to the song and play when the guitar plays 

I

G----5------                                    

D------------   Repeat until you hear the change 

A--3--------

E------------



II

G----8------    Play Once

D------------   Go back to I 

A--6--------  At other times play this then to II and then back to I

E------------



III

G----7-----

D-----------

A--5-------

E-----------

Hope this is not too confusing (Just listen to the song and you'll get it)