一， 主语从句
主语从句在复合句中作主句的主语，常用it作形式主语。引导主语从句的词：that， whether， who, what, which, whoever, whatever, whichever, when, why, where, how等。
It suddenly occurred to him that he hadn’t finished his assignment.
It doesn’t matter whether you hand in your homework this week or next week.
二， 宾语从句
1. 由关联词that引导的宾语从句。
由关联词that引导的宾语从句时， that在句中不充当任何成分，在口语或非正式的文体中常被省去，但如果从句是并列句时，第二个分句前的that不可省略。
He said (that) he was innocent and that should be set free immediately.
2. 由who， whom, which, whose, what, when, where, why, how, whoever, whichever等关联词引导的宾语从句，应注意句子的语序要用陈述语序。
I want to know what he said to you yesterday.
3. 在宾语从句中，引导词whether和if 基本一样，但介词后的宾语从句多用whether。
I will see whether/if she is at home.
Everything will depend on whether the negotiation will go on smoothly.
三， that，what引导宾语从句的区别
在宾语从句中， that没有词义，在句中不作任何成分。当从句意义完整，不缺任何成分时，往往选用that；而what引导宾语从句时，意为“什么” ，有时候可以不译，在从句中作主语或宾语。
You should pay attention to what is mentioned above.
The story tells us that everybody should spare no effort to achieve what he wants.
四， Like, hate, appreciate引导宾语从句
有些动词或动词短语，如like, hate, appreciate,depend on ,see to 等，一般不直接跟宾语从句，需要在从句前加上it。
I would appreciate it if you could take my suggestions into consideration.
I don’t like it when you look at me like that.
五， 表语从句
引导表语从句的词有that， whether， who, what, which, whoever, whatever, whichever, when, why, where, how，because等。
China is no longer what she used to be in the old society.
One reason for her preference for the city life is that she can have easy access to places like shops and restaurants.
六， 同位语从句
同位语从句常放在fact， news， doubt, problem, promise, idea等名词后面，常用引导词有that，who， whether， why， when, where等。
I made a promise to myself that this year , I will make a big difference to myself.
希望我能帮助你解疑释惑。