You have probably heard horror stories about how much losing your virginity hurts. For a few women, it does, but with the right touch and the right partner, you should be able to take his penis into your body without pain. Have him take his time, use a lubricant, and press his fingers into you, opening you up slowly. Tell him when it feels good and when it hurts. What position you use depends on many factors.
Many women prefer to have sex the first time being on top, where they can control the first entry.
Others want to be on the bottom and give their lovers that control. Choose what's best for you. Just remember to tell him to go slow, take your time, and if you feel the need, use a commercial lubricant like KY Jelly. Take a deep breath. Do something else for a while with your hands, your lips and your tongue.