A multi-rotor drone is inherently unstable; left alone it would tip and tumble. It stays level only because an onboard controller senses its tilt and motion many times a second and adjusts the speed of each rotor to counter any drift, far faster than a person could.
This constant correction is what makes a drone appear to hover effortlessly. On top of it sit higher-level controls for holding position against wind or following a path, but all of them depend on that fast, invisible balancing act underneath to work at all.