具体可看链接参考。
from where主要有以下两个用法：
1：引导非限制性定语从句，在意义上相当于and from there（从那儿）。
如：
He hid himself in a tree, from where he could see the enemy in the distance.
他躲在一棵树上，从那儿他可以看到远处的敌人。
2：引导地点状语从句，可视为where前省略了the place，即这样用的from where
相当于from the place where，意思是“从……的地方”“离……的地方”。
如：
From where I stood I could see everything clearly.
从我站的地方我一切都看得清清楚楚。
The car stopped short only a few inches from where I stood.
汽车在离我站的地方仅几英寸处突然停住。
The school was only a few blocks from where she lived.
学校离她的住所只有几个街区的距离。