1、when指时间在定语从句中做时间状语也可做连接词用

I still remember the day when I first came to the school.

2、where指地点在定语从句中做地点状语 Shanghai is the city where I was born.

3、why指原因在定语从句中做原因状语 ，用在reason 后面。 Please tell me the reason why you missed the plane.