Fly reels are pretty straight forward in how they operate. They work on the principle of a winch. An angler takes up line by winding the line, around a relatively small axle by cranking a knob on the face of the reel. To get line off of the reel to cast, you just pull out the line with your free hand while false-casting the fly rod, and as you keep the line moving back and forth with your casting motion, you soon have the amount of free line to cast. At that point, it is just a matter of letting go of the line as you stop the rod on your next forward stroke, and the moving line will pull the loose line in the direction of your forward stroke.