Add them at the end - just before the dish is finished cooking. Otherwise, the herbs will become bitter. Supermarkets carry fresh herbs in the produce section. They come in small quantities and are typically packaged in a plastic container that makes them easier to ship. What herbs you don't use can be stored by standing them in a glass of water inside the refrigerator and covering them with a small plastic sandwich bag or plastic wrap.
Herbs are also incredibly easy to grow.
All they ask for is some sunshine, a little water and an occasional sprinkling of fertilizer. Even if you think you can't grow anything, you can grow herbs. One of the beauties of herbs is that you don't need a lot of space. They're happy in your backyard, but they're just as happy on a balcony, a patio or a window box. Produce stands and farmers' markets sell potted herbs.