There are 9 parts of speech or word classes in English language:
– nouns
– pronouns
– determiners
– verbs
– prepositions
– adjectives
– adverbs
– conjunctions
– interjections

Prepositions function to show:
– relationship in space,
– relationship in time,
– relationship in logic
between two nouns (people, things, places)

The book is on the table.
Preposition ‘on’ in the above sentence expresses a relationship in space (location) between noun ‘the book’ and noun ‘the table.’

We will meet in November.
Preposition ‘in’ in the above sentence expresses a relationship in time between noun ‘we’ and noun ‘November.’

I sent the information by email.
Preposition ‘by’ in the above sentence expresses a relationship of method between noun ‘the information’ and ‘email.’

Prepositions are usually used in front of:
– nouns
This book is for John.
Preposition ‘for’ is in front of noun ‘John.’

– noun phrases (phrases that function as nouns)
This book is for your sister.
Preposition ‘for’ is in front of noun phrase ‘your sister.’

– pronouns
This book is for you.
Preposition ‘for’ is in front of pronoun ‘you.’

If a preposition is followed by a verb, the verb must be in -ing form.
Thank you for saving my life.
Thank you for save my life. (wrong)
Thank you for saves my life. (wrong)
Thank you for saved my life. (wrong)

After talking to the costumer, he went to the meeting.
After talk to the costumer, he went to the meeting. (wrong)
After talks to the costumer, he went to the meeting. (wrong)
After talked to the costumer, he went to the meeting. (wrong)

Prepositions of measure describe quantity, measurement or size of something
– of
– by

of

a bar of chocolate
two kilos of sugar
hundreds of people
millions of dollars
an increase of 2 percent
a third of all people
a third of the city

by

House prices went up by 10%.
Our office floor space measured twelve metres by ten.
Freelance workers are paid by the hour.
This shop sells cloth by the yard.

Prepositions of source describe the origin of someone or something
– from
– by

from

Silvio is from Italy.
They like red wine from France.
The wind is coming from the north.
She took a letter out from her bag.
The Earth receives light from the Sun.

by

This note was written by my wife.
The loud noise was caused by the building construction.
That email was sent by John.

Prepositions of possession describe the ownership of something or the relation between 2 person or things
– of
– with
– to

of

– a friend of mine
– a friend of Mark’s
– the property of my father
– the paintings of Monet
– the role of a teacher
– the director of the company
– employees of the company

with

– married with three children (= has three children)
– a girl with red hair (= has red hair)
– a tall gentleman with a beard (= has a beard)
– a book with a green cover (= has a green cover)
– someone with new ideas (= has new ideas)
– people with plenty of money (= has plenty of money)

to
(is only used with the verb ‘belong’)

This book belongs to Sarah.
Who does this bag belong to?
I don’t know who these shoes belong to.