The cheapie aliexpress specials simply drive the line they're programmed to drive. They have GPS and a gyro to account for the slope of the land. You're supposed to stay in the tractor while they're operating as a safety... but this doesn't always happen in some parts of the world.

30 years ago you had a hand-gas and clamped the wheel to drive the tractor in a line. Using GPS is a litle bit more safe than that. And I talk about Germany!