How do I tell my best friend that I'm bisexual?

Well, I'm bisexual & I eventually ended up telling my best friend my sophomore year. She didn't think I was bisexual. But the best way I could explain to her, was mostrare her a piece of loose leaf paper. I told her took look at the straight lines & the crisp edges. I told her that those lines, are not me. She understood immediately. She accepted me fully with open arms.