A manoeuvring thruster is like a little helper motor on a big boat or ship. Just like you might use your little feet to help yourself turn or move around, a boat needs some extra help to turn or move in tight spaces.
The manoeuvring thruster is like a small engine that gets attached to the sides or front or back of a boat. It helps the boat move to one side or the other really quickly without having to use the big engines that make the boat go forward. It can also help the boat go forward or backwards in tight spots.
So if you are in a really tiny space like a parking lot and you need to turn your car around, you might move your little feet back and forth to help - this is kind of like what the manoeuvring thruster does for a boat!