The common film type is a 35mm for commercial films, but film of 70 mm and greater have been used at times. Occasionally an imax film and camera is used. This film is huge and has a rich picture and sound quality.
That would be the projectonist, who makes sure the film rolls are changed, this does not however apply to digital cinemas, where I can only imagine they start the movie, and makes sure nothing...
A "movie" is actually a very rapid succession of still images, which give the impression of a single moving image. This applies for all movies, including those seen in a computer, in a movie theater...