Difference between How and What

Key difference: ‘How’ and ‘What’ are two questions, which can be used for various purposes in the English language. The main difference between the two is that, how is used to know the manner in which something has happened, whereas what is used to find out about something or the description of a thing or situation.

A question is generally asked to know about something, to understand something, to seek something, to get an answer, etc. ‘How’ and ‘What’ are two such questions, which can be used for various purposes in the English language. However, they differ in the manner that they are used and what type of answers they are seeking.

The main difference between the two is that, how is used to know the manner in which something has happened, whereas what is used to find out about something or the description of a thing or situation. For example: ‘What did you buy at the market?’ I bought a lot of fresh fruits and vegetables. ‘How did you carry it at home?’ My friend gave me a ride home.

Dictionary.com defines ‘how’ as:

In what way or manner; by what means?: How did the accident happen?
To what extent, degree, etc.?: How damaged is the car?
In what state or condition?: How are you?
For what reason; why?: How can you talk such nonsense?
To what effect; with what meaning?: How is one to interpret his action?
What?: How do you mean? If they don't have vanilla, how about chocolate?
(Used as an intensifier): How seldom I go there!
By what title or name?: How does one address the president?
At what price: How are the new cars going, cheaper than last year's models?
By what amount or in what measure or quantity?: How do you sell these tomatoes?
In what form or shape?: How does the demon appear in the first act of the opera? How does the medication come?
The manner or way in which: He couldn't figure out how to solve the problem.
About the manner, condition, or way in which: I don't care how you leave your desk when you go. Be careful how you act.
In whatever manner or way; however: You can travel how you please.
Informal. That: He told us how he was honest and could be trusted.

As seen from the long list, ‘how’ is a word that has many different meanings. It can be used in various manners and asked to get a variety of information. It is generally used to ask the manner in which something has happened, to the extent something has happened or the condition of something.

Examples:

How do you make this recipe?
How could such a terrible accident take place?
How tall is he?
How much for a kilo of grapes?
How is Bill now?
We asked how we could help.
Let me tell you how we'll pay for the trip.
The book tells the story of how the company was founded.
She explained how she came to live here.
I don't know how the service is at the new restaurant.
I remember how they fought.
Be careful how you talk; you could get fired.
She told us how she had to work hard.
He knows how you are a valued employee.
It's amazing how they completed the bridge so quickly.
Better understand the need for clean energy and learn how to be part of the solution.
How to grow and arrange a hydrangea wedding bouquet.
See how to get the look of built-in floating shelves, with less cost and more flexibility.

‘What’ is also a question, but like ‘how’ it has a variety of uses than traditional questions. ‘What’ can be used to refer to various things in various contexts. Dictionary.com lists the many contexts in which ‘what’ can be used:

(Used interrogatively as a request for specific information): What is the matter?
(Used interrogatively to inquire about the character, occupation, etc., of a person): What does he do?
(Used interrogatively to inquire as to the origin, identity, etc., of something): What are those birds?
(Used interrogatively to inquire as to the worth, usefulness, force, or importance of something): What is wealth without friends?
(Used interrogatively to request a repetition of words or information not fully understood, usually used in elliptical constructions): You need what?
(Used interrogatively to inquire the reason or purpose of something, usually used in elliptical constructions): What of it?
How much?: What does it cost?
(Used relatively to indicate that which): I will send what was promised.
Whatever; anything that: Say what you please. Come what may.
The kind of thing or person that: He said what everyone expected he would. They are just what I was expecting.
As much as; as many as: We should each give what we can.
The thing or fact that (used in parenthetic clauses): He went to the meeting and, what was worse, insisted on speaking.
(Used to indicate more to follow, additional possibilities, alternatives, etc.): You know what? Shall we go or what?
(Used as an intensifier in exclamatory phrases, often followed by an indefinite article): What luck! What an idea!
British. Don't you agree?: An unusual chap, what?
Nonstandard. That; which; who: She's the one what told me.
The true nature or identity of something, or the sum of its characteristics: a lecture on the whats and hows of crop rotation.
(Used interrogatively before nouns): What news? What clothes shall I pack?
Whatever: Take what supplies you need.
To what extent or degree? How much?: What does it matter?
(Used to introduce a prepositional phrase beginning with with ): What with storms and all, their return was delayed.
(Used in exclamatory expressions, often followed by a question): What, no salt?
What for; Why: What are you doing that for?

As can be seen by the long list, ‘what’ has many uses. It can be used to ask for a description of something or about something, (‘What is it? What does it cost?’), it may ask about a situation, (‘What is the matter? What are you doing?’), or it may be used as an exclamation or part of a sentence. (What an idea! What, no salt? We should do what we can.’) However, the confusion with ‘why’ arises when ‘what’ is used informally to ask ‘what for’.

‘What for’ is used to ask the reason for something, similar to why. For example: ‘What is the reason for this thing? Why do we use it?’ Both will answer the same thing, however, ‘what for’ is an informal usage and is not grammatically considered acceptable. Still many people use it in normal usage.

Examples: