Many new to the sport think paddling is all about the arms.  Although you can paddle pretty much with the arms, you will tire very quickly if you do so.  Seasoned paddlers use their torso as much as possible to take the load off their arms.  They also push off the foot bulk head with the same side foot with each paddling stroke.  Most of the body works together to get the maximum power out of each stroke.  Here is a good video demonstrating torso rotation: Torso Rotation Demonstration.