This is the main riff. It?s played the whole way through the song. it's pretty easy. 
for the beginner.

E--------------------------------|
B--------------------------------|
G--------------------------------|
D---3-3-3-3-2-2-2-7--------------|
A---3-3-3-3-2-2-2-7--------------|
E---1-1-1-1-0-0-0-5--------------|