We start out with a sentence, see.
1st post
The little girl put her sticky lollipop in her friend's hair.
The next person copies the sentence into their post and replaces one word with a word of their own and puts their word in bold or red or something, so people know what's changed.
2nd post
The little girl put her sticky lollipop in her friend's eye.
Make sure it makes some sort of sense! (ie, replacing nouns with nouns and verbs with verbs, etc)
Here's the sentence the game's going to start with:
The plump donkey ate the purple penguin's face.
Kay? Now have at it! XD