system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why and how do sideways sails work?

While this is a stupid question I can't understand how does a sideway sail on a boat/ship move the ship forward, instead of to the side.
gpt
A sail is a lifting body, like a wing. As long as the sail is in the right position it will generate lift; or create lower air pressure on the outside of the sail than the inside. When this happens the sail will, like an airplane wing, move towards the low pressure side. This creates movement, just like it does in an airplane. 

The reason the sailboat moves forward instead of moving towards the lifting side of the sail is that the sail is connected to the boat, and the boat is in water, and the water has much more resistance than the air. So, the shape of the hull transfers the lifting force of the sail and turns it into forward motion. 

So, a sail is basically an airplane wing that's vertical instead of horizontal, and the sailboat hull is the tool that transforms the sideways pull of the sail into forward motion.