Once you know what the zest is, the question is how to get it off. The layer is very thin compared to the fruit as a whole, but it can be cut off with a knife and then chopped into fine pieces. A more efficient way is to use either a zester (pictured) or a microplane, both of which are tools that slice off only the zest from a fruit. A zester produces long, thin strips that need to be finely chopped, while a microplane naturally creates a very fine chop that needs no further alteration before being added to a recipe.
Unwaxed, organic fruit should always be used if at all possible to avoid introducing any non-food elements into your dish. Fruit juice cannot be substituted for zest, so you will have to use a fresh fruit to get it. Once the zest is removed, the fruit may begin to dry out. Wrapping a zested fruit in plastic wrap will keep it fresh so the fruit can be used or eaten at a later time.
Aside from recipes that already call for it, zest can be added to most recipes, even baked goods, without throwing off the chemistry of the recipe. For example, you can add a teaspoon of orange zest to chocolate chip cookies for a delicious variation or a tablespoon of lemon zest to blueberry muffins to bring out a light, lemony flavor.