I have rarely mentioned these explicitly. And, the walkthrough virtually ignores the ever present monsters in every location that you will have to clear out before safely exploring most locations. Everywhere you go you will find useful scrolls, weapons, health improving items, clothes, armor, etc. Collecting and using such items will be essential to progressing, but I only mention picking up especially significant items which will be absolutely necessary to complete the game successfully. Strahd's Possession is not a linear game, so this walkthrough is only one order of events while many others will also lead to a successful game completion.
Some quests are optional, and have no direct influence on completing the game.
I have included them here as I think they add interest and challenge to the game as well as gain your characters more experience. I have created the following maps from the on-screen automaps from the game. They represent complete layouts. I have marked significant items on the maps. You may still get stuck trying to follow these instructions.