hello andrea how are you ? well in way ............. In the most literal sense, "ON" has to do with contact between surfaces, "IN" has to do with enclosure and containment. The pen is on the book. The book is on the table. The man is on the roof. The newspaper is on the floor. The picture is on the wall. The water is in the glass. The car is in the garage. The students are in the gym. The chocolates are in the box. The milk is in the refrigerator. For non-literal usage, it is not always possible to predict exactly which preposition is to be used. These may have to be learned as expressions. on my mind, on fire, on tap, on the run in a good mood, in trouble, in the way

They are prepositions which have many different uses. I cannot give you a simple answer. There are prepositions of TIME and PLACE, and prepositions that are used with certain idioms and expressions.

Para lugares - in = dentro de On = sobre Para tiempo - in = dentro de