How can you know for sure whether or not you're bisexual?

I have gay and lesbian friends, but I haven’t met a bisexual person before. I understand what bisexual means, but I want to know, how do you know if you’re bisexual or not?
If you enjoy sex with girls and guys, if you’re turned on by both male and female bodies, does that make you bisexual?
And please answer the Q guys, I don’t wanna put this in General.