PREPOSITIONS

Some people do have problems with prepositions.
Do we say 'on the table' or 'at the table'. Actually both are correct, depending on the situation.
For example:
Ali is sitting at the table in the restaurant.
Lily puts a glass of water on the table.

The following words are the most commonly used prepositions:

about, below, off, toward, above, beneath, for, on, under,across,
beside, from, onto, underneath, after, between, in, out, until,
against,beyond, in front of,outside,along,but,inside,over,upon,
among,by, past, up,around, with, at, into,down, through,
before,during, near,throughout,behind,of,to

The information below shows you how to use the prepositions 'on', 'in', and 'at' in different contexts.We are sometimes not sure as when we should use 'at', or 'in' or 'on' as they all sound correct to us.

1. Transportations

I went to Vancouver in my car.
I went downtown on the bus.
We travelled to Toronto on the train.

2. Time

She arrived in February.
I was born in 1988.
I'll be home in three days.
The party is on Thursday.
He left on the weekend.
I'll call you at 7.30.

3. Communications

I spoke to him on the telephone yesterday.
I read about it on the Internet.
I heard the news on the radio.


Source :http://web2.uvcs.uvic.ca/elc/studyzone/200/grammar/prepo.htm