All but a few stars are simply too far away to see as a disk. Yet if you magnify any star image, you will see a small disk. This is the result of diffraction effects. A photo, on film or with CCD, is a time exposure and that introduces a few other considerations, such as air turbulence, that increase the size of this disk. Those topics are covered elsewhere in this chapter.
Light is made up of tiny little particles called photons.
Except they aren't exactly particles in the way we think of particles at human scale. They also behave like little waves. This dual nature is common to the stuff you find at the subatomic level. It gives rise to phenomena that are sometimes non-intuitive. Diffraction is one of those phenomena.