You can look this up online. This question has been answered literally thousands of times before, and is dealt with in every proper English textbook.

Search using these keywords:  <em>difference in on at</em>

After researching, tell us what you understand. :)

   Also Lucy,  regarding the prepositions  IN, ON,  or AT,    see as follows:

http://www.englishgrammarexpress.com/grammar/in-on-at-time

https://www.englishclub.com/grammar/prepositions-at-in-on-time.htm

http://www.esolcourses.com/uk-english/beginners-grammar/prepositions-time/lesson-5/read-and-write.html

  https://www.wisc-online.com/learn/humanities/linguistics/esl2103/prepositions--in--on--and-at

http://www.italki.com/entry/442115

I'm im my bed, on my pillow, at my place. What's yours?

I agree with Michael, but prefer u to memorize them by using in application ...