While not 'equipment' in the traditional sense, Notes and Documents are arguably the most important items you will collect in Amnesia: A Machine for Pigs. These include letters, journal entries, scientific reports, and philosophical musings. They are the primary vehicle for the game's intricate narrative and lore.
Collection and Access: When you find a note, simply interact with it (LMB) to pick it up and read it. Once collected, all notes are stored in your journal, which can be accessed at any time by pressing Tab. This allows you to review past information and piece together the story at your own pace.
Importance: These documents are absolutely crucial for understanding the plot, Mandus's motivations, the nature of the Machine, and the philosophical themes of the game. Without reading them, much of the game's depth and horror will be lost. They provide context for the grotesque imagery, the unsettling sounds, and Mandus's own fragmented memories. They reveal the history of the Mandus family, the industrial revolution's impact, and the dark scientific endeavors that led to the creation of the Manpigs.
Actionable Tip: Always take the time to thoroughly explore every room and area for notes. They are often placed on desks, tables, shelves, or pinned to walls. Some are in plain sight, while others require a bit of searching in dimly lit corners. The more notes you collect, the clearer the horrifying picture becomes.