In restaurant kitchens, a quenelle is an egg shape made by using a spoon or spoons out of soft foods such as whipped cream, ice cream, or fried batters.
Quenelles are perhaps most common in pastry kitchens where egg shaped balls is ice cream, whipped cream, or crème fraiche make for dramatic presentation elements attop plated desserts.
Quenelles can be snapped using either a one spoon push, pull method or with a spoon in either hand passing the item from one spoon to the other while scraping along the edge with the receiving spoon.
When working with whipped crème or ice cream the spoon is run under hot water to facilitate smooth edges in the quenelle. When working with ice cream, a pastry chef will rub her hand against the spoon holding the finished quenelle so that it releases easier.
Specialized quenelling spoons do exist which yield beautiful results and are often employed in fine dining establishments.
When learning to make quenelles, the bottom line is practice makes perfect. Once you make 50 or so and learn the pitfalls such as over heating whipped cream it will become automatic for you. The best way to lean if not on the job is to buy heavy whipping cream, make it into stiff peaked whipped cream, and start making quenelles with a spoon and hot water. There are a plethora of videos out there from which you can learn the technique.