1.作介词：如：I will be back before 7.我七点前回来.
2.作连词：如：I had never seen snow before I came to the north.我来北方之前从未见过雪.
3.作副词：如：Have you ever been to Japan before?你以前去过日本吗?
4.用在习语中：look before and after 瞻前顾后；before all things 首先；before long 不久
5.用在句型中：It won't be long before...不久就...