PREPOSITION IN

In is the most general preposition, It is used to talk about time and location, For exampleIn 1993, In England, In Paris, In the 19th century, In the seventies, In Mandalay, It is also used when something is inside something else, For example the car is in the house

PREPOSITION ON

On is used in a more specific way, It is used to talk about days of the week, streets and avenues, For example, On thursday, On Sunday, On Mandalay 4th street; It is also used when something is above something else. For example the book is on the table.

PREPOSITION AT

 At is used in a little group of things, It is mostly used to determinate hours and locations such as addresses and places, For example: At 8 o'clock, At 3:36 pm, At Cra 72 A N° 3-B, It is also used when something is away of something else, For example look at the car over there.

Here is a video which might help you understand this better

https://www.youtube.com/watch?v=6bs0xMYbUfk