请问英语中since和before具体用法 什么主句过去式、从句什么啦(打个比方)

两者区别应该是很大的,不容易混淆的.
since引导一个过去动作,表示主句动词的持续的发生的动作或存在的状态,从这个时间点开始并持续到说话时（结束或再延续）.
e.g. I have worked in the company since I joined it five years ago.
(I started to work for the compay five years ago and continue to work for it until now. )
A + happen + before B + happen. 的意思已经非常明显了.
e.g. I had worked for another company before I came to work for this company (five years ago).
I won't be long before I am back.= I'll be back very soon.
not long before...不久,很快,时间不长；
The fire went on for 10 hours before the firefighters put it out.
强调：经过了漫长的或艰难的过程,……才……
The accident happened before the driver realized it.
强调：动作发生的迅速：司机还不知道怎么回事/还没反应过来,事故就发生了.