Onions can be prepared a number of ways for recipes, but the most common methods are: saute, caramelize, grill and roast.
The most popular onions at a grocery store are the red, yellow and white varieties.
The yellow onions are full flavored and a great standby for pretty much any recipe. French onion soup is one of my favorite uses for this onion.
The white onion is often used in prepared salads and sauces, and a standby in traditional Mexican food. The red onion, one of my favorites, are great for grilling.