Familiarity is a simulator of virtual communication. The game is a kind of video chat where you will communicate with a girl. During the dialogues you will be offered replicas to choose from. For each of them the interlocutor will react differently.
For all about everything you are given 3 game days. During this time, you should get as much confidence in the girl as possible.
Obviously, you will not be able to open all the endings and achievements from one time. After the 2nd day, the story breaks into 3 branches, each of which will have 2 endings. Choose tactics for yourself.