1.形式主语：即形式上的主语,真正的主语是后面的不定式或者从句.
eg.It's important that we should work hard.
2.非限定性定语从句：即意思上不受限定的定语从句,与限定定语从句相对.区别在于翻译时限定定语从句要翻译到定语的位置上,而非限定定语从句按顺义法翻译即可,在形式上非限定定语从句有逗号,而限定性的没有等.
eg 限定：The girl who is standing there is my sister
非限定：They walked there,which surprised me a lot.
3.同位语：其实就是位置相同,或者说地位相同更恰当
eg; The news that he passed the exam surprised me a lot.这里news与that he passed the exam是同位关系,后者是在解释前者的内容,这也是与定语从句的区别之一.
4.分词作状语：分词的逻辑主语必须与句子主语保持一致,表时间地点方式原因条件让步等.
ed:Being blind,he couldn't tell who gave him the apple.(现在分词作原因状语)
The teacher came into the room,followed by some students.(过去分词作伴随状语)
5.主语从句：即在主句中作主语的从句.
eg:It's important that we should work hard.(形式主语是it,真正的主语是从句)
好像说的还是不是很细,有什么不理解的随时问我!