USE THE PREPOSITIONS: "IN" "ON" "AT"

Prepositions are words that link nouns or various parts of the sentence, denoting the relationship they have with each other, usually used in habitual sentences or in daily life.

At school.

In a house.

On Monday.

The purpose of the use of the preposition is to show the time, the location or introduce an object in a sentence.

IN                         
The preposition in is used to indicate times during the day, months, years, seasons and centuries.

Examples
He started college "in" in 2016.
She attends school "in" the afternoon.
My parents were married "in" the year 2005.

ON
the preposition on is used to indicate days, a particular day, or a particular day and part of it, but being more specific.

Examples
On thursday.
On november 2nd.

On Friday night.

AT
the preposition at we use hours, meal times, holidays and weekends, but being very but very specific and detailed.
I work at the hospital.
At 12:00 p.m. is the lunch hour.
She travel at the sunday.