The Game menu lets you control the status of the current game:
Finish the actual game set and start a new session with new tiles.
Pauses the entire game, especially the timer which affects the scoring. The menu entry then changes to Resume Game, which is used for resuming the game.
Shows the (local) Top-Ten charts of Shisen-Sho.
Show a tip, which two tiles to remove next.
Restart the current game with the same tiles.
Shows a dialog which tells you whether the game is solvable or not. If the menu entry Disallow Unsolvable Games in the Settings menu is checked, this option is absolutely useless.
Some of the menu items can also be controlled by hot-keys. See the section called “Key Bindings” for a list.