In and at
Both at and in can be used with the names of cities, towns and villages. We use in when we are talking about the place as an area; we use at when we see it as a point.
Compare:
- My sister lives in Tokyo.
- Our plane stopped at Tokyo on the way to Iran. (Tokyo = Tokyo airport)
We use at to talk about group activities and shops/workplaces.
- I first met him at a party. (NOT …in a party.)
- There weren’t many people at the meeting.
- I saw him at the baker’s. (= baker’s shop)
We use in with the names of streets and at when we give the house number.
- He lives in MG Street.
- He lives at 128 MG Street.
We use on when we think of a place as a surface.
- The cat is lying on the floor.
- Hang this picture on the wall.
Till and until
Both till and until are used of time.
- We waited till / until 12 o’ clock.
- He slept till / until 11 am.
Since
Since is used before a noun or phrase denoting some point of time. It is preceded by a verb in the perfect tenses.
- He hasn’t eaten anything since yesterday.
- He has been ill since last Monday.
- It has been raining since yesterday.
In
In is used before a noun denoting a period of time. It means ‘at the end of’. Within means ‘before the end of’.
- I shall return in an hour. (= at the end of one hour)
- I shall return within an hour. (= before the end of one hour)