Sub/Dom Relationship

Hello all, I am 21 years old and I am in a new relationship with a man that is 26. He recently told me he was interested in being submissive in a sexual sense. Personally, I have only had sex with one man, four times. I am pretty inexperienced in the sex department. We have great chemistry and really like each other. But I am scared. I have never even considered being dominate and being in a Sub/Dom relationship. Does anyone have any advice? I don't want to run away because he is a good guy. He's informed me that if I decide I am not into that kind of relationship he would be okay with that and we would make it work. Any advice? Help!!