The "ordinary world" to Salvatore takes place in a small village in Sicily. The most frequented place by the locals is a cinema that shows mostly Western films, black and white. The time is around the 1930's and 1940's era, Salvatore is just a small boy with an acute fascination with movies, especially the projection booth.
Salvatore meets his "mentor figure" early on. It's the projectionist Alfredo. A much older man than Salvatore, eventually they become close friends. Alfredo teaches Salvatore about moviemaking, life, love and philosophy - things that Salvatore will never forget.
The "crossing of the threshold" basically is the persistence of Salvatore. One day Salvatore's mother is beating him for not buying milk, instead going to watch a movie. Alfredo witnesses this and comes to the rescue by convincing his mother that Salvatore just lost the money, and Alfredo found and paid off his mother. This was a turning point for Alfredo, by helping a child that he turns away nearly every day.
Salvatore is constantly "testing" Alfredo's patience. This makes the story very real, as small children usually test the patience of adults, mainly teachers. Salvatore already has his strongest "ally", Alfredo, but is falling in love with a girl named Elena.
"Approaching the inner-most cave" happens the day of the graduation exams and Alfredo and Salvatore are both taking the same exam. Alfredo is in need of help, he can't remember the answers so he signals Salvatore. Together, the two make a silent pact, Salvatore will help Alfredo pass his test, and Alfredo will teach Salvatore the wonders of moviemaking.
The "supreme ordeal" is when the film (in those days made of cellulose nitrate, highly combustible) begins to catch fire and sets the projection booth aflame. Alfredo is caught in the flames...