I'm preparing to overplay a game soon but the phases are still fuzzy to me.

I'm preparing to overplay a game soon but the phases are still fuzzy to me. Could someone explain how they flow from one to the other, and how the rogue phase differs, content wise, from a perilous phase? Do the phases blend throughout a narrative unit? Let's say the rogues are discovering the world, and danger appears: do I switch straight to a perilous phase?