Staircases allow people to reach places that are of a height higher than they currently are, they allow access to places that are otherwise unreachable. The most common place you will find a staircase is in a house, any property that has more than 1 floor will contain 1, this will allow you access to the floor above.
There are many different types of staircases and the standard ones found in homes are simple and straight, they go up at an angle in a straight line, however there are variations to these and are often found in larger properties with a lot more space. The curved staircase is a variation and looks amazing, it has the exact same purpose but is manufactured and installed in a different way. The case goes up at an angle but instead of going in a straight line it curves round in a certain direction, the main reason these are used is for their aesthetic design, they look expensive and really add character to the property. They are also found in other properties like schools, museums and other large establishments.
The curved staircase can be enlarged even further and be turned into spiral (helical staircase), these are one again curved in appearance but instead of having one curve that they go all the way round into a spiral and essentially going up in a vertical line. There are 2 instances when these are used, the first being in restricted space where a diagonal staircase would not fit and the other in Abbeys, Mansions and other grand places where the staircase is required to go up a great height, not only do the extend to great highest but look exquisite.