Hi, I'm a students and I confuse how to makea differences of using at, in, on...

please help me
Here is a summary taken from Purdue Owl ( https://owl.english.purdue.edu/owl/owlprint/594/ ):

Point in time:

On is used with days:
I will see you on Monday.
The week begins on Sunday.

At is used with noon, night, midnight, and with the time of day:
My plane leaves at noon.
The movie starts at 6 p.m.

In is used with other parts of the day, with months, with years, with seasons:
He likes to read in the afternoon.
The days are long in August.
The book was published in 1999.
The flowers will bloom in spring.


To express notions of place, English uses the following prepositions: to talk about the point itself—in; to talk about the surface—on; to talk about a general vicinity—at.
There is a wasp in the room.
I left your keys on the table.
She was waiting at the corner.

For more details, look farther down the page at the link I gave above.
Thanks for your explanation about that..
Students: We have free audio pronunciation exercises.
I will meet you in the hotel on Monday at 12 noon.

He arrived at the airport on a mule and made the mistake of leaving the mule's plane ticket at home, in the garage, on top of the freezer.

At, on and in are prepositions and begin a prepositional phrase. To understand if the word is a preposition, place in a sentence. And if that sentence makes sense, then it's a preposition.

She flew _____ the clouds. So.... She flew (at, on, in) the clouds makes sense, or at least a grammatically correct sentence.