When a shutter is pressed and the aperture opened, light enters the camera lens based on the aperture size.
The aperture is composed of blades that expand or contract depending on how much light the photographer wants to let into the lens.
Contracting the aperture blades into a smaller opening lets in less light and increases the depth of field in the image. This means a larger range of distance in the scene will be rendered as in focus.
Alternatively, when one opens the aperture blades, we get a larger opening and more light would be allowed in. This would create a more shallow depth of field, meaning more of a scene in front and behind the focus, the point is out of focus.
The shape of the aperture blade determines the basic shapes of these points. Rounded blades will produce more round bokeh, while angled blades will produce a different look.
Having more aperture blades will generally give a lens a rounder aperture and smoother bokeh than a lens with fewer blades. Lenses are often marketed with the number of blades and the quality of having beautiful bokeh, which is sometimes described as smooth and creamy.
The Bokeh depends on the following:
Aperture opening
Blades in the camera
Full frame capabilities
F-stops
Good lenses have more blades and smaller F stops and full-frame capabilities.
