When

When
When 然后；可是；当 ... 时
And they roared when Seaman held up two fingers.
然后当希曼伸出两根指头的时候他们就吼叫起来。
I stayed till noon, when I went home.
我留到中午，然后就回家了。
When all is said and done, we still must eat.
可是说到底，我们还得吃饭。
But when I returned the door was open.
可是回来时门是开着的。
How can they learn anything when they spend all their spare time watching television?
他们把所有的空闲时间都用来看电视了，还能学什麽东西呢？
It was the sort of morning when everything goes wrong.
那天上午就是那样，事事不顺心。
He entered on his inheritance when he was 21.
他21岁时继承了财产。

详解：

when可用作从属连词,引导状语从句,表示时间时作“当…时,在…的时候”解; 表示条件时作“如果,要是”解; 表示对比时作“既然,考虑到”解。当when所引导的从句的主语和主句的主语一致时,常将其主语、系动词或助动词省去,只留实义动词或表语,或者改写为短语。
when所引导的时间状语从句用一般现在时代替将来时,用现在完成时代替将来完成时。
when有时也可用作疑问代词或关系代词,作介词或动词的宾语。例如:
We'll get there heaven knows when.天知道我们什么时候才能到达那里。
Next summer, by when the house should be ready.到明年夏天房子就准备好了。

Unless<-->While