The Difference Between "On" and "In" in English

The difference between the prepositions “on” and “in” in English:
Differentiating between “on” and “in” is especially difficult for native speakers of Spanish because there is only one preposition for both: “en.”
In English, we denote “on” when saying something is on top of something else. We use “in” when saying something is inside of something.
“On” and “in” are not replaceable!

For example:
He is in the classroom.
This means that he is inside of the classroom attending class. If we replaced in with on, the sentence would not make sense, unless the classroom has a room and someone can be there.
She is on time.
Meaning she has arrived on time. Since no one can physically be inside of time, they must be on it. Think of it like the person is floating above the point on the watch.
It is on the table.
This means that the object is on top of the table.
It is in the table.
This is only possible when there are drawers inside of the table. For example, the napkins are in the table. If the table does not have any drawers, then this is not possible.
What’s the difference between “on” and “in” in the following sentence?
The drink is on the car.
The drink is in the car.
The first one means that the drink is on top of the car, probably on the roof.
The second one means that the drink is inside the car, probably in the cupholder.

I hope this helps make the difference between “on “ and “in” in English more clear!