It is installed on the edge of wall to:
Protect the wall edge from chipping or wear
Provide a smooth and round surface
Improve safety by giving a more visible wall edge
Give a neat, finished look to tiled or wooden wall edges
Where it’s commonly used
Tiled staircases
Wooden wall edges
Concrete stairs (with adhesive or screws)
The curved lip you see is designed to sit over the front of the step, while the flat side sits on top of the stair surface.