Sorry for the unfinished state leaving so many questions open. Once your first follower has been sent to recruit more (top middle icon), you can drop new cultists on various tasks around the den, some of which are unlocked later - the Necronomicon cannot be written by a caveman but only a high level mage later on, for example. It is meant ot be a scarcity system so don't be disappointed if your entire cult is eaten in the fifth round. Some new follower will turn up eventually.