The rules are simple. You post something like:
Person 1: I ate cookies for breakfast.
The next person:
My real name is Jean
Person 2: Liar. You ate two hippopotamuses and five elephants.
I killed my best friend.
So basically, you post a sentence and the next person pretend you've lied (you are allowed to lie) and change it. Simple.
So, I'll start.
I have just stolen all the cookies out of your cupboard.