as the others have said, try it out yourself first so you become comfortable with the feeling of it, then when your boyfriend does it, have plenty of kissing etc before hand and just take it slow and go with the flow. you should'nt bleed as most girls hymens break in early puberty just from dancing, horseriding, cycling etc but it my feel very sensitive and maybe uncomfortable at first...just relax and only carry on for as long as you feel comfortable to do so xx