Tokens, Placeholders, and Variables

I would love to know the differences between the three. From what I understand, tokens are fields that can be called on when displaying, calculating, or manipulating data?

But then I read about placeholders? Then to get really confused, I see I can add varibales such as %site_name or %username when creating messages.

I wanted to create a custom message for a user so I created an action with a trigger. Then I added some tokens in [brackets] to that message and the message displayed the actual text of the token, not the token itself. It looks like I should have added some variables?

I was blonde prior to being bald :)

James
IWasBornToWin.com