how should I use "at ""in "on"?

how should I use "at ""in "on"? I would like todo know it. This is so confusing.

This is a complicated question to anwer because we use these three litlle words as prepositions of time and of place. 

At work. In a taxi. On the menu. = Place

At 5 0'clock. In two weeks time. On 3rd August. = Time

This is a brief explanation.  Why not book a trial session with me and I'll explain it further.