There're three known endings in the game so far.

To get this ending you have to finish the game normally. This is the default one so there's no much explanation needed here, except going through the game from start to the end and keeping the right path during the final chase.

During the final chase we must disobey Gregory's instructions and turn left after the 3rd split. After that you have to quickly run ahead to Freddy's cardboard cut-out in the cave and put on the mask when close to it.

To get this ending, you have to find 4 hidden cameras in the game. To access them first you need to zoom out the minimap on specific consoles and just click on the camera that was not visible on the minimap while it was zoomed in. Image from this camera is easy to recognize because it show doors to some unknown location. After clicking on hidden camera the doors will open and then you can exit the console.

Secret cameras locations:
Chapter 1 - Monty's Minigolf, this is the first console in the game. After short tutorial just zoom out the minimap and click on the camera that was not visible while minimap was zoomed in.
Chapter 3 - Monty's Catwalks, 2nd last console in this stage, it's located before the AR tunnel and close the chair node.
Chapter 5 - Console is located after we get out from the barber shop and after the 3rd node (Big scissors). This one is visible only in AR mode, so first put on the mask and then quickly access the camera. Note: It's better to do this before solving the puzzles because after solving them there's no way to access it again, unless we repeat the level.
Chapter 7 - Bonnie Bowl, the last console is located in the far left side of the map when we enter the big room with bowling area to the left. It's gonna be next to bunch of music-mans, but don't worry they don't bother so just access the console, zoom out minimap and click on hidden camera.

For more details check out the video.