Basil is an annual plant, so you need to let it go to seed, which means the seed pods will turn brown, open and scatter the seeds. Best way is after the pods turn brown, make a little sack w/ gauze or cheese cloth and thread. Or you could watch until the pods start to open, cut them off, open them up and get the seeds. Sort of a pain, basil seeds aren’t too expensive. But the pods must be brown.