Theory:

A proper noun, like any other noun, the word must be a person, place, thing, or idea.
Nouns that refer to specific people, places or things. Proper nouns like Nepal, Stella, or White House are capitalized.
Example:
1. Mala went to the mall today. (person's name)
2. Rama bought her favourite mango juice, Tropicana. (brand name)
3. It reminds her of the home as this juice is bottled in China. (place)
Important!
Proper nouns have two unique features:
 a) It names a specific or a "one-of-a-kind" person, place, animal, event, or thing
 b) It always begins with a capital letter, regardless of its location in the sentence.
Simple, its main function is to state the actual name of a specific person, an animal, a thing, a place, or an event.
Reference:
partofspeech.org/kinds-of-nouns-proper-nouns/