at is a preposition, most commonly translated in French by à. It locates a point in time or space. Unlike to it is never used with motion verbs like come or go (or welcome).
- at 8 o'clock, (be) at the train station
- at night (NB: in the morning / afternoon / evening)
It is also used in many idiomatic expressions:
- at best / at worst: au mieux, au pire
- at ease
- at risk
- at will