Gmaj - Amin - Bmin - Cmaj
This song also happens to be in the key of G major, which we can establish by analyzing the chords. The above progression, when analyzed numerically, is: I - ii - iii - IV (which then repeats). After this part is repeated, the song continues:
F#dim - Bmaj - F#dim - Bmaj - Emin - Amin - Amin - Dmaj
(Don't know how to play diminished chords? Here are some common diminished chord shapes.)
Continuing to analzye in the key of G major, the above progression is vii - III - vii - III - vi - ii - ii - V. There is one pesky detail about this progression, though; in the key of G major, the third (iii) chord should be Bminor, when, in this case, it's Bmajor. This is our first example of a songwriter's use of chords that fall outside of the major key that he/she started in. Exactly why the above progression works, and sounds good, is beyond the scope of this article, but it is important to note that many songs use chords other than just the seven chords in it's key. In fact, one of the factors that makes a chord progression sound interesting is it's use of chords that don't directly belong to it's key.