The forward stroke is the one you will use the most.  It looks deceptively simple but takes time and practice to truly master.  In ACA terminology, they use the acronym CPR - Catch, Propulsion, and Recovery.  Most novice paddlers butcher this stroke by bending their arms and simply using their biceps to move the paddle.  Many also have the infamous death grip on their paddle.  Both of these mistakes will tire you out in just a few hours.  Paddlers with great technique use their torso muscles instead.  They also use their arms like a pair of fairly rigid struts - very similar  to a ballroom dancer's form.

More resources to help with the forward stroke:

This is another good example that emphasizes the use of the torso and releasing at the hips:  The Forward Stroke.

For another example of this critical stroke, the following video is from Mike Aronoff at CKAPCO: The Forward Stroke.