It is used to indicate location, inclusion, or position within spatial, temporal or other limits 
- As a preposition of place - meaning
- As a preposition of time - referring to:
- Years, e.g. in 2011
- Centuries, e.g. in the 20th century
- e.g. referring to parts of the day with the; in the morning, in the evening, in the evening, in the night (but note also at night)
- e.g. to express a time point that will happen in future time after a definite time period, e.g. in ten minutes, in three weeks.
- the past, present and future; e.g. in the past, in the future.