The key to effective public speaking is preparation. The better you prepare, the more confident you will feel.
Preparation begins with identifying your audience. What do you know about your audience? What do they care about? What’s important to them? Do they have any misconceptions about your topic? These are the kinds of questions you should ask as part of your preparation. Sitting down and listing the questions, and your answers to them, will give you a basic structure for your speech, around which you can add things and take them away as you see fit.
Holding the attention of an audience and speaking to what interests them is the most important thing about any public speech. It is not merely about what you say, but also how you say it. If you have a message you wish to get across, then think of how that message will communicate itself best to the audience you are speaking to.