Bearded iris from seed
If you want to grow iris from seed let your iris go to seed -- don't deadhead. Leave the seed pods on the plant until they are brown or deep tan and dried and ready to split or beginning to split. Collect the seed heads open them and collect the seed.
Prepare a sunny part of your garden by removing all weeds, and loosening the soil.
Plant the collected seed about 1/2 to 3/4 " deep and water in carefully. Do this in the fall when temperatures are beginning to drop. Keep your collected seed in a cool dry spot until ready to plant. Continue to water this area but not to the point of sogginess until the ground freezes. In the spring at least half of your planted seed will hopefully sprout. Your seedlings will look like grass at first until they begin to grow and take on the appearance of young iris. At that point you can transplant them anywhere you want in your garden that gets the sun they like and is moist but well draining. Good luck