how是连词,因为它是个副词,所以又叫做连接副词.有两个用法.
一是单独使用,意为“怎样,如何”,在后面的从句里做方式状语.如：
He asded me how he could get there.他问怎样到那儿.how表示方式.
二是后面跟上一个形容词或副词（副词正是用来修饰形容词或副词的）,两词一起在从句里做相关成分（如果单独说,就是how 用来修饰后面的形容词或副词）.如：
He asded how many people there are in my family.他问我家有几口人.how many用来修饰people.
many是个形容词.
He asked how much (money) tha coat was.
He asked how fast I could run.他问我能跑多快.fast 是个副词,how fast 用来修饰谓语run.