KIKI, you've got a long way to understand their usage thru reading relevant articles or topics (in fact, it's not just only for business english that you must know their differences... it applies to all). here, try to figure out which between these sentences is correct? 1. My boss is IN the office. 2. My boss is ON the office. 3. My boss is AT the office. :)

Prepositions of Place: at, on, and in We use at for specific addresses. Grammar English lives at 55 Boretz Road in Durham. We use on to designate names of streets, avenues, etc. Her house is on Boretz Road. And we use in for the names of land-areas (towns, counties, states, countries, and continents). She lives in Durham. Durham is in Windham County. Windham County is in Connecticut. http://grammar.ccc.commnet.edu/grammar/prepositions.htm

Prepositions of Time: at, on, and in We use at to designate specific times. The train is due at 12:15 p.m. We use on to designate days and dates. My brother is coming on Monday. We're having a party on the Fourth of July. We use in for nonspecific times during a day, a month, a season, or a year. She likes to jog in the morning. It's too cold in winter to run outside. He started the job in 1971. He's going to quit in August.

see my comment...

Your question is way too general.