Hi emmy13. You are quite young to get into the D/s scene. I'm not criticizing you, just stating facts. The things said by Jds4med are correct but may not go far enough. Do not get involved with a Dom whom you do not know very well. Talk to his friends if he will let you, if he will not let you talk to his friends, run, don't walk, away from him. Spend a lot of time on "vanilla" dates, no hanky-panky on these dates and a lot of talk. If, after many dates and talk about life in gerneral and speaking to his friends, you still feel comfortable, take it to a different level of conversation.
Speake about his desires as a Dom. Keep asking around the question until you get a straight answer! If you get so much as one "bad feeling" get out! Talk to him about what he expects of you as his sub and keep digging until you feel comfortable. Remember, one "bad feeling" can turn into serious physical and psychological harm, be careful. Then question him about follow up care after a session as his sub. Be sure that you understand that you will need and want care and that he is not only willing but eager to give it.
Read up on D/s and on follow up care; this is important! You have to know where this may lead.
After all of the above, if you feel 100% confident that he has your best interst at heart, go into the subject of "safe words" very carefully. Be careful if he has mentioned gagging or blindfolding you, these activities can lead to serious harm. Then, if you are completely satisfied, discuss your first session, location, length, bondage etc and be sure that he will not go one step beyond what you agree on!
Again, if all the above is OK with you, try a first session but let a friend know what you will be doing, with whome, where and when. From then on, I hope that you develope a comfortable, safe relationship.