According to the National Onion Association (NOA), they are best stored in a cool, dry, dark and well-ventilated room, such as a pantry, cellar, basement or garage. This is because they easily absorb moisture. If temperatures or humidity are too high, they may start to sprout or rot.
Cooking Guidelines
Add chopped or sliced onions and cook for 5 to 7 minutes or until tender, stirring frequently with a wooden spoon or heatproof spatula. That's how long to sauté onions to remove the harsh onion flavour and just barely start to sweeten the cooking onion.