I know you can "fill" crepes or pancakes I guess you could call it. You just take the filling, whether it be fruit compote, salsa or sausages and spoon a small bit of "filling" into the center of the crepe or pancake. Then fold the sides over the filling and flip it over with the folded side resting on the plate. Dust or sprinkle with cinnamon, powdered sugar, whipped cream, salt and pepper or fresh chopped herbs. All depends on what you are filling it with.
Canolis and doughnuts (sp?) are a different matter. It's more like "injecting" with a filling when it comes to these.