on
Days of the week - on Monday
in
1. Months / seasons - in August / in winter
2. Time of day - in the morning
3. Year - in 2006
4. After a certain period of time (when?) - in an hour
at
1. For night - at night
2. For weekend - at the weekend
3. A certain point of time (when?) - at half past nine
since
From a certain point of time (past till now) - since 1980
for
Over a certain period of time (past till now) - for 2 years
ago
A certain time in the past - 2 years ago
before
Earlier than a certain point of time - before 2004
to
Telling the time - ten to six (5: 50)
past
Telling the time - ten past six (6: 10)
to / till / until
Marking the beginning and end of a period of time - from Monday to/till Friday
till / until
In the sense of how long something is going to last - He is on holiday until Friday.
by
1. In the sense of at the latest - I will be back by 6 o'clock.
2. Up to a certain time - By 11 o'clock, I had read five pages.