So in the song peggy sue how many of each chord do I strum ?  Thanks.

Hi,
I'm a newbie to the site and have a really simple question.  If I choose a song, say...Peggy Sue:

http://www.chordie.com/chord.pere/www.g … /8499.html

I see the chords but how many of each do I play (whats the timing) and at the end of the fourth line whats going on here? Why are all the chords squashed together (G C G D7)

Any advice really appreciated from a complete novice.

Thanks,
Sean