Game Credits work a bit differently here than you might expect, but are still simple enough to understand. First, you must understand that Thermopylae Online is just one game in a number of online games that belong to the Empires of History Online Gaming Network. With a free account you get 4 game credits, but these credits may be used on any games within the Empires of History Online Gaming Network, not just Thermopylae Online.

When you sign up to a game it is like you are giving us a token (credit). While you are participating in that game we hold your game credit. When your game is over, or in the event of multi player games (more than 2), when you are eliminated from the game, we return the credit to your account and you may use it again. So by having 4 game credits with a free account you can play in up to 4 ongoing games on a regular basis.