Sex help ASAP

My bf and I are had sex for the first time and he kinda had a hard time keeping his dick in me while he was thrusting how does he keep it in? And the sex kinda felt good but not really only just a little bit and he said he he felt the same but barely what do I do how do we make our sex better for both of us ? Do u recommend any positions that give him the max enjoyment and me the max enjoyment? Help