Most people think of public speaking as a very formalized event, but really, there are many instances in life in which we might be called upon to speak publicly, and so at least an acquaintanceship with public speaking principles and some practice at doing so is important.
Certainly, at school, students are called upon to speak publicly, with "Show and Tell" in kindergarten being only the beginning. In many work settings, people are called upon to make presentations, to speak at meetings, or to speak on behalf of their employers in public. In one's private life, there can be plenty of public speaking, at weddings or funerals, for example. People belong to various kinds of organizations that require them to speak publicly, as well. And as members of communities, people speak at school board meetings, at "town halls" of various sorts, and at hearings that are open to the public. People are called upon to be witnesses at trials sometimes, too.
No matter what the nature of the public speaking, the keys to doing well are organization and preparation. I always tell my speech classes there are three parts to a speech: tell your audience what you are going to tell them, tell them, and then tell them what you told them. Present your main idea, support it, review it for your audience, and then sit down. There is really little difference between preparing a speech and writing an essay. If you have done your spadework and you organize your material, you are prepared to do both.
public speaking is nessessairy because if you watch the kings speach you will see that sometimes you are put in a situation that you didn't expect to be in. for example:
your friend matthew will be saying the graduation speach but then he dies and you are forced to take his place well then you will see why public speaking is important!
hope it helps