How brakes are applied to Space ship to reduce its speed or to stop it when it is travelling in space?

Retro rockets.
Basically a force applied in the opposite direction.

Reverse rockets, turning rockets, turbothrustogizmogimbals.
Parachutes when landing.
Airbags.
Anyone could build one.

Personally I think a Rocket is like an Airboat, Do a 180 and apply full thrust?
Ever play Asteroids?