From Grey Olltwit Software:
On the first screen choose the Play or Load A Saved Game button.
Choosing Play will take you to the preparing game screen. The periodic table is divided into horizontal lines called periods. Each game highlights one of the nine period lines so you can think of periods as levels of the game. Once the line is highlighted you are able to start the game. At the top of the screen you are shown an element name. You have an air gun, like at a fun fair, and your mission is to correctly hit the element symbol name on the line of the periodic table. A cross hairs aimer is shown and follows the mouse pointer. Just place the aimer over the element symbol you believe matches the element name and left mouse click to fire. If it is correct the element symbol will spin and you will receive 100 points. A bonus is also available depending on how quickly you hit the correct symbol. The bonus value is shown on the left and decreases the longer you take. If you make a mistake, the correct symbol and atomic number is show with the element name. Once you have correctly hit all the symbols you get four choice buttons. You can play the Next Period, Try Period Again, go to the High Score Table or Save Game. Clicking Save Game opens a window file browser where you can type a name for your saved game and click Save.