一、用作介词，表示在...上；向，朝等含义。
The book is on the table.
书在桌子上。
The spider is walking on the ceiling.
蜘蛛在天花板上爬行。
They made their own judgment on his report.
他们凭他的报告作出自己的判断。
二、用作副词，表示向前（移动），进行着等含义。
Put your coat on.
穿上你的`大衣.
Move on!
向前走！
She worked quietly all night.
她整个晚上默默地继续工作。
三、用作形容词，表示在进行的，在发生的等含义。
The televisionw set was on.
电视机开着。
The light were all full on.
灯火通明。