Prepositions show a relationship between two words or phrases in a sentence.
On, at, and in are prepositions of time and place.
Using the prepositions for times -
Use in for parts of the day (the morning, the evening), seasons, months, years, long periods of time (the fifteenth century)
Use at for points on the clock (three o'clock, noon), points in the day (lunch, midday, sunrise)
Use on for singular or plural day of the week (Friday, Wednesdays), dates (December 25, 2000), special dates (my birthday, your anniversary)
Using the prepositions for places -
Use in for neighborhoods, villages, cities, countries, and places with a boundry.
Use on for streets, avenues, courts, drives, islands, large vehicles (trains, ships, buses), surfaces (the table, the floor), electronic devices (the phone, the computer, the laptop)
Use at for specific addresses (123 Anywhere Ave), specfic locations (the top, the bottom, the corner, home, school, the grocery store)
These are general guidelines. There are exceptions.