Onions are the most vegetable we use the most for every meal so knowing the difference is important.  There are about 21 different types of onions but the most common onions used in cooking a typical African dish are the yellow and red onions.

Yellow Onions
These are usually relatively cheap and available all year. The yellow onions have a bit of sweetness to them with strong flavor. They caramelize nicely and hold up well when cooked. Unless your recipe states a specific type of onion, this is the default onion for most dishes.
You can use yellow onions to cook any meal, but they work really well in dishes that require long cooking times or as the base in stews, stocks and for soup (blended with peppers). They're great for boiling meat and chicken as well.

Red Onions
 The red onions are more expensive and some people consider them sweeter for cooking. While you can cook with it, it’s less overpowering than the yellow onions, making it ideal for uses that require raw onion.
The red onions add a nice color to whatever they’re added to and so are great grilled with fish or sliced thinly as a topping for Suya, sandwiches and salad since they don’t leave you with onion breath and aren’t super strong.

Storage Tips for Onions

In the refrigerator:  Store in a single layer in the vegetable bin on paper towels.  Or, for longer storage, wrap in foil.

In pantyhose:  Take a leg from a pair of clean, sheer pantyhose, drop an onion into the foot, tie a knot and repeat as necessary.  Hang in a cool, dry, well-ventilated area.  Cut above the knot when ready to use.

On racks or screens:  Place on elevated racks or screens, not touching, in a cool area.

In the freezer:  For long-term storage, sweet onions can be frozen, but their texture changes so frozen onions should be used only for cooking.  Chop and place on a cookie sheet and place in the freezer.  When frozen, place in freezer containers or bags.  To store whole onions, peel, wash, core and freeze in a freezer-proof container or bag.

Drying:  Chop and dry in the oven, using the lowest setting.  Remove when thoroughly dry but not brown.  Store at room temperature in airtight containers.