从句,就是从属于句子的句子.
例如：Tom is doing his homework.这是一个简单句.那当我们表达复杂一点儿意思时,例如：我想说,住在我家附近的Tom,那就需要这样来表达：Tom who live near my home.这里who.引导的就叫定语从句,因其在名词后修饰名词.修饰名词的词叫定语,修饰名词的从句叫定语从句.整句可写成：Tom who live near my home is doing his homework.
宾语从句也是如此:Tom says that he will come soon.that 从句是say 的宾语从句
不知这样讲你是否明白.看多了就懂了.别着急.