How do cameras work?

Cameras are of two types

Digital:

These cameras have photo sensitive transistors which actually help to generate different voltages for different colors of light and they get converted to different values through a ADC and are processed to generate a picture.

Older cameras:

They contain silver compound (mostly Agcl) coated reel (photo reel which we buy) which is exposed to atmosphere for a split second when the shutter opens and thus by different intensities a different pattern is formed producing a photo. That is the reason negative cleaning is done is dark rooms.
There are several type of camera but a still digital camera captures an image and stores it as a data file. A still film camera captures light images on a light sensitive film which can then be developed into photographs.