Once you have these three chords down. you will be able to move ahead on playing, and start into Barre Chords. 

[G]Mama [D]take this badge from [Am7]me
[G]I can’t [D]use it any[C]more
[G]It’s getting [D]dark too dark to [Am7]see
[G]Feels like I’m [D]knockin’ on heaven’s [C]door

[G]Knock knock [D]knockin’ on heaven’s [Am7]door                                             [G]Knock knock [D]knockin’ on heaven’s [C]door
[G]Knock knock [D]knockin’ on heaven’s [Am7]door
[G]Knock knock [D]knockin’ on heaven’s [C]door

[G]Mama [D]put my guns in the [Am7]ground
[G]I can’t [D]shoot them any[C]more
[G]That cold black [D]cloud is comin’ [Am7]down
[G]Feels like I’m [D]knockin’ on heaven’s [C]door

[G]Knock knock [D]knockin’ on heaven’s [Am7]door
[G]Knock knock [D]knockin’ on heaven’s [C]door
[G]Knock knock [D]knockin’ on heaven’s [Am7]door
[G]Knock knock [D]knockin’ on heaven’s [C]door