How do you tell your parents that you have your first boyfriend?

Ask them to talk, sit them down and just tell them. Unless your very young it won't be very unexpected, it's normal for people to date. If one of your parents is stricter than the other it might be best to tell them first and have them help you tell the other or even tell them. A lot of people tell their mothers first.

You might get some resistance but only because they care about you (although you might just think they are interfering), and they have vast experience of the dating scene from their own dating years. Just remember your parents and their friends were dating people when they were your age, you haven't just invented it nor has it changed. But if you ask them how their parents dealt with them and their first date, they may have a more reasonable approach to yours.