Scallions provide a subtle onion flavor to salads without being too overwhelming.  To store, simply place in a plastic bag and keep in the hydrator drawer of the refrigerator.  Use within a week.
To prepare, trim off roots and 1-2 layers of outer thick leaves until you reach the white inner stalk.  Wash the whole scallion in a bowl of cold water and gently mop dry.  Chop into rings, sticks, diagonals, or whatever size you would like for your recipes.  In addition to being used raw in salads or as a garnish, they are excellent in stir-fries, soups, and stews.