Each year we save our seeds from the previous years plants. Most of our medicinal herbs are perennial, meaning they come up each new Spring by themselves, the roots can survive through the winter. These plants are propogated by either taking herbal cuttings and letting then sprout or digging and dividing sections of their roots and replanting.
There are a few however which are annual. They need to be reseeded each year, mimicking what they would do in nature. Normally they would dry up and drop their seed, which would then germinate when the conditions were right the following year.
These are the seeds we generally start in trays, then transplant at the appropriate time outside. Principally the ones we use are Calendula and Chamomile. We might also start some of the perennials that we are lacking at the same time.