The fizz that bubbles up when you crack open a can of soda is carbon dioxide gas (CO2). Soft drink manufacturers add this tingling froth by forcing carbon dioxide and water into your soda at high pressures—up to 1,200 pounds per square inch. The "fssst" you hear is millions of carbon dioxide molecules bursting out of their sweet, watery prisons, where they have been held against their will.
An unopened soda can is virtually bubble-free because the pressure inside the can keeps the carbon dioxide dissolved in the liquid.
When you crack open the can, you release the pressure and allow the gas bubbles to wiggle free from the liquid and rise to the surface. This requires energy because in order for the gas to break free from the liquid it has to overcome the force holding the liquid together.
One way to input energy is to shake the beverage. This adds the zing needed to unleash more tiny bubbles and add real splash to a celebration.