I realize that 0,0,0 technically isn’t a “number” as I say in the video. But it shares the qualities of what a number is. It is a placeholder of a value. In this case the value is a position in space. This position in space (0,0,0) is often called the origin, and when learning to 3D model, it is one of your best friends. It will help you get oriented, offer you a central location to “snap” to, and acts as a measurement point whenever you need one.
If you’d like a further dive into coordinates, I recommend reading this entry from Wikipedia: “Coordinate System“.