Here's a quick tutorial:

Your objective is to gain as many crucifixes and holy books as possible, in order to save yourself from the Nun or the Demon's punishments. Gathering these will be a challenge, as you are being actively chased by the Nun, and the demon sometimes attacks you.

GATHERING ITEMS

1. Hold click the yellow circles. Those are the light levels, allowing you to see the books and crucifixes better.
2. Click on the books and crucifixes to collect them. Some are harder to see than others.

AVOIDING ATTACKS

1. Click on the demon before she slides into your screen. She may also run at you from the front of the chapel, and if she reaches you, you will be prompted with a time-based minigame.
2. Don't let the nun get to you by reaching the end of the chapel before she reaches you. To see where she is at, click the "Turn around" arrow at the bottom of your screen, or "S" on your keyboard.

CHOOSING YOUR FATE

Choosing your fate will depend on what you have or don't have in your inventory. If you don't have enough items for any option, you must surrender, ending your run. Otherwise, you will be sent to the next phase.