“On” is the more general and inclusive preposition, and generally can be used in place of “upon” in nearly all situations.
“Upon” is a less common and more formal preposition used when referring to occasions, events or abstract situations, but not normally referring to physical objects: you would not say “Please put the coffee cup upon the table”, for example.
E.g.
the occasion of his eldest daughter’s wedding, he gifted the couple with a manor house in the country.
her mistress.
(“On” would also work in either of the above sentences, being the more general of the two prepositions.)
