Only the host can actually start the game. This is because the host may have sent out invites and may be waiting for specific players to join. If you are not the host, all you can do is set your initial orders and then wait for the game to begin.
As the game host, it is up to you when to start the game, but don't keep your players waiting too long. If the "Start Game" button on the game detail screen is not available to you, then it means one of two things:
You don't have enough players. When you created the game, you chose the minimum number of players allowed. The game will not allow you to start the game until at least that many people have joined. So keep waiting for more people to join, or invite more players.
Your players are not ready. Look at the list of players. If one or more of them have "Not Ready" next to their name, then it means they have not set their initial orders, so the game cannot start. It can't start because the system doesn't know which of that players ships to use and how to position them in the battle. Send a reminder message to any players who are still "not ready".
Once both of those conditions are met, the "start game" button will become available. Once it is, you may click it to start the game.
After you have started the game, no more players may join. Also players will not be able to change their initial orders. You also may not invite more players after this point.
Once the game is started, the "Launch Game Client" button will become available.
Next topic: The tactical interface
