.. How does the "notes" function work?

The notes function, which was called the case file or notebook in previous games, is now on Rosa's phone, along with her email and internet research capability, and is indicated by a pen icon.

The notebook serves two functions: it lists subjects Rosa can bring up when talking to others, and it can be used to combine two ideas to create a third one. (For example, if you had "I'm thirsty" and "Water fountain" as subjects, combining them might result in "Get a drink.") There are a couple of places in the game where you have to help Rosa draw these kinds of conclusions to move the action along; look in these hints for help if you get stuck.