Moving a conductor in a magnetic field creates a current in the conductor.
A flowing current creates a magenetic field that opposes the original fixed field.
The force between them slows the conductor down.
To make a brake simply put a big magnet on the moving vehice and to stop move it near a fixed big lump of metal. It's advantagous are that theres no contact between the magnet and conductor so no friction, no wear and no noise.
On things like rollercoasters it's handy as a failsafe, if you mount metal plates under the car and put a fixed magnet at the end of the track (or the other way round) you don't have to rely on a brake being activated - the car will sow down when the two come together.