The only place that makes you a great Public speaker is the mirror. You just take any topic from anywhere, memorise it and stand in front of the mirror and say it without looking at the paper. Public speaking is not about making yourself comfortable in front of public but it is more about being comfortable with yourself. If you have stage fear then to check, do just one thing go and stand in front of the mirror and try to speak on any top-ic , you will realise that problem is not the public but it lies somewhere within. So, there are many channels on Youtube that you can watch like letstalk podcast and many public speaking courses for free but they will just guide you but the confidence will come only when you practice.