at or during a time earlier than (the thing mentioned)

You should always wash your hands before meals. 饭前应该洗手。

Before leaving he said goodbye to each of them. 走前他和每个人都告了别。

She's always up before dawn. 她总是黎明前就起床了。

Before he could reach the door, she quickly closed it. 他还没走到门前她就迅速关上了门。

Before we make a decision, does anyone want to say anything else? 趁我们还未作决定，还有人想说什么吗？

She had to give the doorman a tip before he would help her with her suitcases (= he would not do it until she had given him a tip). 她得给看门人小费，好让他帮她提箱子。

until (the event mentioned)

It was an hour before the police arrived. 警察一小时后才赶到。

in the past

He said he had never seen her before. 他说他以前从没见过她。

I feel as though I've been here before. 我感觉好像以前来过这儿。

in front of

The letter K comes before L in the English alphabet. 在英语字母表中，K排在L前面。

Many mothers put their children's needs before their own. 许多母亲都把孩子的需要置于自己的需要之前。

We have the whole weekend before us - what do you want to do? 我们有整个周末的时间——做些什么呢？

He stood up before a whole roomful of people, and asked her to marry him. 他在满屋子人面前站起来向她求婚。

If a place is before another place, you will arrive at it first when you are travelling towards the second place.

The bus stop is just before the school. 公共汽车站就在学校前面一点。

If something is before someone or before a group of people, it will be formally considered or examined by that person or group.

The proposal before the committee is that we try and reduce our spending by ten percent. 委员会正在考虑我们打算降低10%开支的建议。

The men appeared before the judge yesterday. 这些人昨天出庭了。