Closet

Hello, I am 18 years old and mostly still in the closet. My friends mostly know that I am pan, but none of my family do. I know they will be accepting of it, since I also have two gay cousins and they get treated normaly and supported. Still, I am hesitant since many people I met online, often said things like 'pansexual doesn't really exist. It's just being bi.' wich hurt. I know I'd have to explain the word and the kind of sexuallity it is to my family. Now... I don't know how to come out. How do I tell them. How can I explain it to them?