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)

We use ‘at’ for the time of the day.
at 10 a.m.
at 2 p.m.
at 5 o’clock

We use ‘at’ for a specific time in a day.
at noon
at night
at midnight
at dinnertime

We use ‘at’ for a specific time in a week (British English).
at the weekend
at weekends (= every weekend)

We use ‘at’ for certain holiday periods.
at Christmas (during Christmas period, not only December 25 specifically)
at the New Year (during New Year period, not only January 1 specifically)

We use ‘on’ for dates.
on August 1
on ApriI 1, 2022
on August 17, 1945

We use ‘on’ for specific day in a week.
on Friday
on Monday
on Tuesday

We use ‘on’ for plural or repeated days.
on Saturdays (= every Saturday)
on Fridays (= every Friday)
on Sundays (= every Sunday)

We use ‘on’ for a specific time in a week (American English).
on the weekend
on weekends (= every weekend)

We use ‘on’ for specific days/dates.
on your birthday
on New Year’s Day (= on January 1)
on Christmas Day (= on December 25)

We use ‘in’ for parts of the day.
in the morning
in the afternoon
in the evening
(for night, we use ‘at night’)

We use ‘in’ for months.
in April
in January
in December

We use ‘in’ for years.
in 1835
in 2020
in 2035

We use ‘in’ for seasons.
in (the) spring
in (the) summer
in (the) fall
in (the) winter

We use ‘in’ for centuries.
in the nineteenth century
in the 15th century
in the eighth century

We use ‘in’ for duration.
in 20 minutes
in ten minutes
in an hour
in two weeks