1. In - Can be used to show general locations like neighbourhoods, cities, countries and places with a boundary
For example: I live in India. / We will be staying in a hotel tonight.
2. On - Can be used to refer to more specific locations like streets, avenues, islands, surfaces and large vehicles
For example: Latha stays on the fourth floor. / The book you are looking for is on the rack.
3. At - Can be used to refer to very specific locations
For example: You can find us at the park. / She is at home now.