First day back to school, why do I feel so different from everyone?

I personally have felt very abnormal, I know that I am not an abnormal person but the way how teens at my school have have countless relationships, can just go up to people and say hello full of energy. I want to obtain that level of socializing where I can be cool with everyone, I only have two friends that I could consider real friends, but the others I talk to we don’t consider our friendship outside of school. How can I become someone that everyone would like to get along with