why do i feel nervous in front of public and how do i overcome nervourness

this topic in the blog,about the nervous in public.everyone know when first time speak in front of public maybe afraid and the same time i feel what the our feel.i afraid because the public can not understand what i talk.i afraid the public laugh to me and like me stupid.i'm shy because afraid the public protes my speak.then i afraid what i talk wrong topic.i can not barrier communication.beside that i not confident what i talk and lack information about speaking.then how do i overcome nervousness,i can learn in front of mirror.i can ask what i don't understand the talking about.i can read English book and understand what i read.beside that, writing in english and give commitment in english class.