At the start of each level, you are presented with an overview of where you are in your progress of the game, with respect to the ultimate goal: the chamber atop Astaroth's tower.
You begin your game far to the left, in the cemetery. You must travel through each stage, and defeat the boss at each stage's particular checkpoint in order to progress to the next.
Each stage differs in topography and enemy content. There are also many hidden items that can be made to appear in each stage by passing through the right location. This Walkthrough will illustrate each of those locations for both the Arcade version, and the Famicom/NES version.