When you hear a sound, you become aware of it through your ears.

If you hear something such as a lecture or a piece of music, you listen to it.

If you say that you can hear someone saying something, you mean that you are able to imagine hearing it.

If you hear from someone, you receive a letter or telephone call from them.

In a debate or discussion, if you hear from someone, you listen to them giving their opinion or information.

If you hear some news or information about something, you find out about it by someone telling you, or from the radio or television.

If you have heard of something or someone, you know about them, but not in great detail.

If you say that you have heard something before, you mean that you are not interested in it, or do not believe it, or are not surprised about it, because you already know about it or have experienced it.

If you say 'Do you hear?' or 'Did you hear me?' to someone, you are telling them in an angry or forceful way to pay attention to what you are saying.

If you say that you can't hear yourself think, you are complaining and emphasizing that there is a lot of noise, and that it is disturbing you or preventing you from doing something.

If you say that you won't hear of someone doing something, you mean that you refuse to let them do it.