how to know people?

i just found out that all my life (17 years) all the people ïve considered my friends didn¨t really knew me, not my interest nor the things i liked or disliked,they never truly knew what my personality was like,they all just saw me from the surface, and it was the ame thing from my side, i didn¨t knew them, i tried to but just couldn¨t,so someone please tell me, how do i get to know someone?