Prepositions are those words which are used to link nouns and pronouns
They tell relationships between different words
The book is on the table.
Here, book and table are nouns
“ On ” is a preposition which tells relationship between “book” and “table”
He is in the car.
Here, He is a pronoun and car is a noun
“ In ” is a preposition which tells relationship between “He” and ‘car”