The main loop of the game is as follows -

Go to work at the local library via a terminal there. Pick one of several jobs and then head home after getting paid.

After every 7 'days' of working an event will come through which will continue with the story.

There is a day and night system which can allow access to various shops and places of interest around the city.

There are side quests within the public library's notice board that you can take, however, they are time sensitive. So after every 'main' event you finish check the board.

Following this, there are 3 'main' side quests that can be interacted with via gene splicers, aka the furries of this game.

WHICHEVER OF THE FIRST SIDE QUESTS YOU INITIATE THAT INVOLVES ITS FIRST SCENE WILL DETERMINE THE FINAL BOSS OF THAT SIDE QUEST.

There are five endings in the game:

1. Complete the game as normal.

2 - 4. Complete any of the three main side quests to their respective endings.

5. Complete the Deep Sea Devil's side quest, and then the haunted mall side quest to its totality. 

These endings are linear in nature, meaning, if you complete objectives for #5 you will only get that endings, the same with 2-4, so if you want to see everything make multiple saves before you start on 2-4.