Hello, Let me introduce a little bit more complicated grammatical structure with "how" and "what", relative clauses: You say something + I don't understand = I don't understand WHAT you say. He told me his name + I forgot it = I forgot WHAT his name is. I want to say something + I love you = WHAT I want to say is I love you. You are doing something + That makes me angry = You are doing WHAT makes me angry. There is a machine + I can't use it = I don't know HOW to use that machine. I learn Chinese + People wonder how = People wonder HOW I learn Chinese. You watched a film + You know how it was = You know HOW the film was. As you see, you can make clauses by using "how" and "what" (also which, when, etc...) "How" indicates the way of doing something. "What" refers the object itself. "Which" refers to a feature of that object (Remark the difference with "what") : There are options + Choose the best one = Choose the option WHICH is best. I want a watch + Like the one I bought for my friend = I want a watch WHICH is like the one I bought for my friend. She sings a song + She heard that song at a cafe = She sings the song WHICH she heard at a cafe. I want a car + That car is expensive = I want a car WHICH is expensive (The same meaning with "I want an expensive car) Your question is very general, I hope these help :)

Hello yinghuajudy, "how" and "what" are adverbs both used for interrogation. How You ask about the manner ,the way or by what means something is done or is being. How did you prepare this meal? How are you ? It means also to what extent, amount or degree. How big is the place ? How tall is she ? 'How' is used also to indicate delight, surprise or a strong feeling : How interesting ! How wonderful to receive that gift from you . What It asks about the purpose ,asking questions regarding persons or things such as: What is this? What did you say? It is used in asking for the specification of an identity, quantity, quality, etc. It also asks to specify actions ,deeds etc What is your job? What is his address ? Some other examples: How was your day ? What did you do today? How can I help you ? (in what manner) What can I do for you ? ( specifying the action) How can I learn English ? ( by what means) What can I do to learn English? ( specifying actions ) How big is the house? ( to what extent or degree) What is the size of the house?( asking for the specification of a quality). In this example the interrogation is almost about the same thing in the 2 sentences. Both adverbs 'how' and 'what' are used here in different sentences structures giving the same context.