It's kind hard to explain so I'll give you an example.(please don't feel bad if i use you as an example!)
TNP stands for The Next Person.

ginnyweasleyfan:Truth
zanhar1:If you had one wish what would it be? Dare.
LivinLife:I would rule the world.
I dare TNP to kiss the computer screen 10 times. Truth.
lovebaltor:*kisses screen 10 times*(you have to do it!)Who was your first kiss?Dare.
mdigs73:A girl at my school named Mary. I dare TNP to go up to a random person and yell in their face:"WHO ARE YOU CALLING CRAZY!?"

And it goes on and on and on. So basicly whatever you say(truth/dare) is what the next, next person has to answer/do. OK, I'll start.
I want a truth.