Onion

Onion is a vegetable grown worldwide. It is related to garlic and leek.

Some recipes suggest you use a particular type of onion. Still if you keep many types of onion on hand either you must buy small amounts which is usually less economical or they will deteriorate in storage. If a recipe calls for one type of onion and you've only got different onions:
 * You can try it with the onions you've got, perhaps adapt it and don't repeat it if it doesn't work out.
 * You can go out and buy the onions the recipe suggests.
 * You can go online and look for a different recipe that works with your onions.

Storage
Onions store well and keep for a month easily in a fridge. Still onions start to deteriorate after they are cut. If you buy onions of different sizes together you can often find one the size you want for the recipe you're doing. If a recipe calls for just half an onion and you don't want to throw the other half away you can cut the other half up, bag it and freeze it. That way later when you need another half onion you've got half an onion cut up and ready to use.