I learned some prepositns today. I basically understand the uses of some prepositions.

1. in, at , on when they express locations.

in: to express sb or sth locats inside of a location, not exact.

at: to express sb or sth locats a exact location.

on: to express sb or sth locats surface of a location.

Examples:

I just arrived at the train station.

I just arrived at a building of the train station.

I just arrived on a square of the train station.

2. until, till, before, by

untill's meaning equals till. to express the duration ofamovement; by expresses a movement completed last time.

Examples: I am going to work until( till) seven tonight.

I am going to complete work by seven tonight.

I am going to work before seven tonight.