How to Use a Zester
Kitchen zesters are small instruments with tiny holes, made to create thin strips from foods like citrus fruits, onions, ginger, chocolate and hard cheeses. They're nice to have around because they're a lot easier (and safer) than the small knife you'd otherwise need for the same function. (A veggie peeler or a cheese grater can also work in a pinch, but they're not ideal.)
First, make sure whatever you're going to zest is firm. (Otherwise, the zester will just kind of push into it without really working.) You can always put the item into the freezer for a minute or two to firm it up.
Do your zesting on top of a cutting board so that your shavings fall onto something clean.
Hold the zester in your non-dominant hand, and press it into the cutting board at an angle. With your other hand, move the food up and down the zester. If you're working with a piece of fruit, move it circularly and then down and only zest the colored portion. The white part underneath (pith) is bitter.
When you're done zesting, make sure to rub the opposite side of the instrument off -- food tends to get stuck there instead of falling onto the cutting board.