P.O.E.T. Blog Tip #2: How to use IN, AT, and ON

1. This is how to use AT in a sentence:

Where's Taka?
He's at work.
He's at school.
He's at a conference.
He's at home.
He's at the movies.
He's at the beach.

2. This is how to use ON in a sentence:

Where's Wuhan?
She's on the phone.
She's on a call.
She's on her lunch reak.
She's on vacation.

3. This is how to use IN in a sentence:

Where's Sam?
She's in a meeting.
She's in class.
She's in the hospital.


Reference:
http://www.americanenglish.state.gov