Green onions are just young, tender onions. You can eat the entire thing, white bulb to green tip.
Store green onions in an unsealed bag in the refrigerator.
Be sure to wash green onions well. Cut off and discard any root remaining on the bulb, and any parts of the top that have turned yellow or brown. Slice the green onion into discs. You can eat the entire thing raw or cooked, but think of the green tops like herbs, and the white bottoms like a regular onion. The green tops can be added as garnish or at the end of cooking, while you can saute the sliced bulb anywhere a recipe calls for an onion. The dividing line is up to you – experiment and see what you like!