How to insert penis into the vagina ?

I'm 24 yr old male. I had seen so many porn. I saw that the guys insert their penises directly into vagina during the screaming of their partners & sex harder .. & harder hurting them.
This is my first time having sex with a girl. So now I fear/shy about sex with my partner, I want to know correctly, how to insert my penis into the vagina ? & how I sex with her without hurting ?
So, what should I do ?