This stroke is called a “sweep”, “back sweep”, or “J stroke” depending on who you’re talking to. Whatever the title, it is a steering stroke used in the stern of the canoe.
As you will see in the diagram below, a sweep on the rightside of the boat will turn the boat right and a sweep on the left side of the boat will turn the boat left.
To preform a back draw, insert your paddle directly behind you so that the paddle is basically parallel to the side of your boat, and close enough to the canoe that it is almost touching.
Your upper body should be twisted around, shoulders parallel with the side of the boat.
From that position, sweep your paddle around until it is perpendicular with the boat, then remove it from the water and prepare for your next stroke.
From the perspective of speed and/or efficiency, the back sweep should be used sparingly because, while it is a very effective steering stroke, it will slow down (or even stop) your forward progress.