Some edible plants benefit us in more than one way. The dill plant is one of those. The fern-like leaves can be used fresh or dried and are usually called Dill Weed. The seeds are also used but for a stronger dill flavor, usually in pickling. (See Garlic Dill Pickled Okra and Garlic Dill Pickled Carrots on the Canning Information page of Pantry Cooking Plus.)
Dill plants form “heads” of flowers that turn into seeds, first green, and then brown as they mature and dry. Once they turn brown, each “head” can be cut and used fresh when making dill pickles or they can be allowed to dry so that the seeds can be removed. Be sure to cut them when the flower stems are still green or starting to turn brown so that the seeds stay on them when you cut off the “head.”
For more information on drying the seeds, see the Drying Dill Seed page of Pantry Cooking Plus.