While playing against the computer in play game mode you can resign the game or ask the computer for a draw.
You can resign a game by selecting the Play->Resign menu item. When you resign a game you are giving victory to your opponent, the game will be over. You should resign if your position is hopeless and you believe your opponent is strong enough to prove the win.
You can offer a draw to the computer by selecting the Play->Offer draw menu item. Depending on the computer's assessment of its position it will either agree to the draw to reject your draw offers. If the computer wants to play on it will inform you as follows:
You should play on as the computer does not want a draw.
If the computer agrees to the draw you will see:
The game is now finished.