You use how to ask about the way in which something happens or is done.

You use how after certain adjectives and verbs to introduce a statement or fact, often something that you remember or expect other people to know about.

You use how to ask questions about the quantity or degree of something.

You use how when you are asking someone whether something was successful or enjoyable.

You use how to ask about someone's health or to find out someone's news.

'How do you do' is a polite way of greeting someone when you meet them for the first time.

You use how when you want to say that it does not matter which way something is done.

You use how to emphasize the degree to which something is true.

You use how in exclamations to emphasize an adjective, adverb, or statement.

You use how in expressions such as 'How can you...' and 'How could you...' to indicate that you disapprove of what someone has done or that you find it hard to believe.

You use how in expressions such as 'how about...' or 'how would you like...' when you are making an offer or a suggestion.

If you ask someone 'How about you?' you are asking them what they think or want.

If you say 'How about that?' you are drawing attention to something that has been said or done that you think is surprising.

You use how about to introduce a new subject which you think is relevant to the conversation you have been having.

You ask 'How come?' or 'How so?' when you are surprised by something and are asking why it happened or was said.

If you say 'How do you mean?' to someone, you are asking them to explain or give more details of what they have just said.

If you say 'How's that?' to someone, you are asking whether something is acceptable or satisfactory.