Looking for information on world generation seeds? See Advanced world generation.
Seeds are used in farming. They can be stored in bags (100 seeds per bag), which can in turn be stored in barrels or pots (10 bags per barrel/pot). Different seed types can't be mixed within a bag, so storing 10 seeds, one each of 10 different types, would require ten different bags. Seeds can be brought on embark, obtained by gathering or growing the respective crops, or by trading. When crops are eaten or used in brewing, milling or plant processing, they typically leave one or more plantable seeds. The exceptions are valley herb, bloated tuber, kobold bulb, and muck root, which will not leave behind seeds after processing. Cooking in a kitchen will not produce seeds when plants are cooked, even under the limit.
There is a cap for number of seeds: once there are 200 seeds for one kind of plant, no seeds will be generated by either eating or processed in workshop that uses plants (saving a number of hauling jobs). Hitting the cap does not prevent player from buying extra seeds from traders.