how和what

what是疑问代词，和介词连用，例如：what does she look like?what is she like? how通常不用于和介词连用，它可以和系动词连用，例如：how does she look? how is she ? 此处look,is都是系动词。what does she look like?what is she like? 通常用于对长时间的特征提问，例如：what does he look like? he is a handsome young man. how does she look? how is she ? 通常用于对身体状况或临时特征提问，例如：how does she look?she looks puzzled. how is she ? she is ill with a bad cold.

how是副词，如果句子不缺成分就用how；what是代词，必须充当句子里一个成分。