in on at 在preposition of place

in:
Country, city or district (e.g. China, HK, Tsuen Wan)Enclosed place (e.g. classroom, bedroom, hall of school, lift)Small vehicle (e.g. car, taxi)"the sky"
at:Building (e.g. hospital, school, mall, cinema)A point but not a place (e.g. bus stop, entrance, corner)"home" Address (e.g. 13 Nathan Road)
on: Street (e.g. Nathan Road)Surface (e.g. wall, floor, paper)Large vehicle (e.g. train, bus, ferry, minibus, MTR, plane)
*有時你會發現building都會用"in",因為你真係想講o係o個幢野入面, e.g. I met Judy in the school./ I found my wallet in the school.
以上只係最基本ge分辨方法,特殊用法另計(e.g. in jail= 坐緊監)

我推薦您一個非常不錯的英語學習網站，里面有很多非常不錯的學習資源：

http://www.hkenglishstudy.info

希望可以幫到你!