Having good communication skills is important. They can help you with presentations in class, during job interviews, when handling arguments, and in a variety of other situations.
Some people think of projecting their voice as pushing to make it louder, but that only causes strain to your vocal cords, exacerbating the problem. Instead, you want to make your voice larger
In a nutshell, it is not knowing what will happen when you are in front of people, giving your speech or presentation. Your fear is not that you don't know your topic. It is that you don't know what will happen when you step to the podium or table.
If you want to become a great speaker, you should first have an idea on what it means to be great. Famous speeches became that way in part because the speaker knew how to wring the most feeling and meaning out of what he was saying.