What is the Quadtree Algorithm?

[LN7oGNh0]

Ive read a lot about this, and I want to use it in the game im making at the moment, but I dont really understand it. I understand that it splits into four squares continuously until it has reached the highest depth, but I dont know how to use this in my game... If I were to make a Quadtree class, what are some basic functions that is should have? Lastly, this is my first game, so is this a bit too complicated?

Thanks