A radio-controlled boat is like a toy boat that you can control using a little remote control. Just like how you can control a toy car or helicopter with a remote, you can use a remote control to make a boat move, turn and stop.
The boat has a little receiver inside it that receives signals from the remote control. These signals tell the boat what to do. When you move the joystick on the remote, it sends a signal to the receiver in the boat which then makes the boat move in that direction.
The motor inside the boat is what makes the boat move. It is kind of like the engine in a car - it spins the propeller which propels the boat forward through the water. If you want the boat to turn, you can use the remote control to make the motor spin the propeller in a different direction.
Some radio-controlled boats are very small and can be used in a shallow pool, while others are bigger and can be used in a lake or ocean. Some are even so big that people can ride in them!
Whether you are racing these boats with friends or just having fun during a day at the lake, controlling a radio-controlled boat is a fun way to enjoy being out on the water.