The Whole Thing is basically just:

G, C, Em, D

but Barre plays it like this

G (320003@1)               C (x32010@1)         Em (022000@1)        D---------------------------------------------------------| (xx0232@1)------12-12--12-----5--5--5------8--8--8-----7--7--7-----|
------x--x--x-------x--x--x------x--x--x-----x--x--x-----|
------12-12--12-----5--5--5------9--9--9-----7--7--7-----|
-/10--------------3------------7----------5--------------|
-------------------------------0-------------------------|

Then when it comes to the "who knows, who knows, who knows?" u just hold on to that D 
shape and then at the end of the chorus where it goes "guess i need some time" etc, you 
repeat the C shape and the D shape - First tab so go easy