从句是什么意思通俗点

人有主要人员和随从人员之分,那么句子除了主句之外也有随从的句子这个就是所谓的从句,它的作用是对主句的主语宾语进行进一步说明（这个有主语从句和定语从句）：
1、the reason that he told me was not reasonable（定语从句）
the reason why he can not go to school is that he is ill （同位语从句和表语从句）
why he can not go to school is that he is ill（主语从句和表语从句）
she told me the reason that he did not go to school（定语从句修饰宾语）
2、状语从句
if he is ill,the party will be put off（条件状语）
because he is ill ,the party will be put off（原因状语从句）
when he went to bed,his mother was chatting over QQ（时间状语）