How Do You Be Yourself And Not Care What People Think?

I need some help to be more popular iknow this might kinda be a girly site, But any help is good in my position. OK so all i need to know is how to be myself and not care what other people think and be loud in class but i`m to shy i always ask my friend how he does it and he alwayse "Just dont care what people think about u" i say "How" and he says "It`s to hard to explain" so if anybody here can explain please Post