怎样区别主句和从句

先找关键的动词
定语从句：we often think of the days that we spent together on the island.
主句是完整的,而从句是不完整的,需要先行词作为从句中的主语,宾语,状语成分,从句一般是that which where who等引导词后面的句子
宾语从句：He said that he would go to beijing.
宾语从句的主句是不完整的.需要引导词引导的从句充当某一成分
that he would go to beijing.是said的宾语
状语从句：从句在整个句子中做状语,如：
My mother was cooking when I arrive home.
当我到家的时候,妈妈正在做饭.
when I arrive home.作为一个时间状语,修饰cook,因而叫做状语从句.
主句完整.从句是时间,原因,地点等状语