The first poster gives 5 letters in order and the person to follow makes a 5 word phrase out of it using those letters to start each word. They then leave 5 new letters for the next person and so on.
Here's some examples:
Me: W W Y L T Bizzaro: Why Would You Leave Tanzania. P P T L N Frank: People Prefer To Live Naturally
And so on...
Bandit OP wrote
A E G T H