Gelatin in thin transparent sheets (or leaves) weighing precisely 2 grams is the form used in France. They are available from specialty stores or online. To use them, soak them in a bowl of very cold water (unless otherwise specified) for about 10 to 15 minutes, until they are softened and very pliable. Then remove them from the water and squeeze all the liquid out with your hands. Dissolve them in the quantity of warm liquid specified in your recipe, stirring until there are no visible traces left. Follow the recipe instructions for setting or jelling times. Note that gelatin is an animal-derived product; should you prefer a plant-based jelling agent (such as agar-agar), follow the instructions on the packet for quantities and times.