名词性从句包含：主语从句,宾语从句,表语从句,同位语从句.从句中的that只起引导作用,没有意义,也不做任何成分.宾语从句中常省略.whether、if引导名词性从句起引导作用,还有意义“是否”的意思,但不充当成分；不能引导定语从句.疑问词引导名词性从句,疑问代词what, which, who做主语,宾语,表语；疑问副词where, when, why, how在从句中做状语.前面不一定有名词；what不能引导定语从句.
定语从句属于形容词性从句,作用相当于形容词.其中出现的名词叫做先行词,that, which, who, whom, whose叫做关系代词,指代先行词,在从句中要充当成分,这就是区分它和名词性从句的关键.where, when, why叫做关系副词,在从句中做状语.
例如：You should hand in all that you have.（定语从句）
You should hand in what you have.（宾语从句）
It is an honor that she was chosen as the monitor.（主语从句）
We heard it that she would get married.（宾语从句）
The king’s decision that the prisoner would be set free surprised all the people.（同位语从句）
The king’s decision is that the prisoner would be set free.（表语从句）
注意细节.还有不懂的话 再问