Types of Onion

Yellow Onions

The workhorse, the staple, the everyday brown beauty, yellow onions are suitable for any conceivable use, other than perhaps as a garnish for your martini (use a pearl onion for that). You could easily live a rich and fulfilling life even if this were the only onion you ever tasted.
Its heavy brown parchment skin surrounds ivory white flesh with a strong, sulphury, pungent flavor and aroma. If a recipe says onion without specifying what type, it's assumed to be a yellow onion. Use them for making French onion soup.

Sweet Onions

Larger and slightly flatter than yellow onions, with lighter colored, less opaque skin, sweet onions contain extra sugar, making them good for caramelizing. Their larger size and sweeter flavor make them ideal for making onion rings. Sweet onion varieties include Walla Walla, Maui, Vidalia, as well as others with the word "sweet" in the name.

White Onions

White onions have a papery white skin, and their flavor is milder and sweeter than yellow onions, making them good for serving raw in fresh salsa or homemade guacamole.The onion can be sautéed to a dark brown color and served to provide a sweet and sour flavor to other foods. Small white onions used in soups, casseroles or stews, they are known as 'boiler onions'.They can also be added to salads.

Known sweet white varieties include 'Walla Walla', 'Vidalia' and 'Mauri'. White storage onion types include 'White Wing' and 'Sierra Blanca'

source :https://www.thespruceeats.com/uses-for-different-onion-types-4008831