How did staircases and ramps help defend castles?

Answer 1

Staircases in castle towers always turned counter-clockwise. This had the result that the usually right-handed defenders - most often the ones standing above - always could use their left arm to steady themselves against the wall and they could use their right arm to wield their weapons; this was also the side where there was the most room to swing them.

The attackers on the other hand apart from having to fight upwards, had their right arm and in most cases also their weapons on the side of the wall which made swinging them difficult. And the fact that they could not fight and use the wall for balance at the same time put them at a further disadvantage. With the absence of railings, losing your balance meant falling to your death.

A ramp (a gently sloping passage to a higher level) was mostly useful to wheel catapults and later, cannon to a defensive position instead of having to haul them up the stairs.