1. where指地点，在定语从句中做地点状语用来表示地点的定语从句。
(1) Shanghai is the city where I was born.
(2) The house where I lived ten y ears ago has been pulled down.
2. when引导定语从句表示时间。在定语从句中做时间状语也可做连接词用
(1) I still remember the day when I first came to the school.
(2) The time when we got together finally came.
[注]表示时间"time"一词的定语从句只用when引导，有时不用任何关系代词，当然也不用that引导。
By the time you arrived in London, we had stayed there for two weeks.
到你到达伦敦的时候，我们在那里已经待了两个星期。
I still remember the first time I met her. 我仍然记得我第一次见到她。
Each time he goes to business trip, he brings a lot of living necessities, such as towels, soap, toothbrush etc。
每一次他去出差，他带来了生活必需品，如毛巾，肥皂，牙刷等，很多。
3. why指原因 在定语从句中做原因状语
(1) Please tell me the reason why you missed the plane.
(2) I don"t know the reason why he looks unhappy today.
注意：关系副词引导的从句可以由"介词+关系代词"引导的从句替换