Time to flower your plants.
Flowering: Once your plants go into the flowering room with 12 hours of light, 12 of dark they will spring up from several inches to feet depending on the height of the original plant. Depending on the variety it will be 8-12 weeks before they are ready to harvest. While you can harvest early it reduces the amount of material you will end up with.
Now that you have a general understanding of what is needed you can look online and order seeds. Seeds are currently legal under federal law so go ahead and order pretty much without worry in most states. There is plenty to choose from and kinds to choose from.
Fertilizer use – Generally speaking if you are using good dirt you won’t need fertilizer regardless how big you grow the plants. I’ve used everything from Bat shit to fish emulsion and nothing has been able to really make a difference. The same is true for adding CO2 into the room. With regular air exchanges in the room to control temp and humidity the environment already has twice the amount of CO2 that the plants can use..
Harvesting is in another class.
Types of Seed: find more details about seed here
There I hope that gives you the basics of growing cannabis indoors.