What do they stand for?
There's the נ, read "Nun" and pronounced /n/. This stands for Nes, miracle.
Then there's the ג, read "Gimmel" and pronounced /g/(hard). This stands for Gadol, great.
Then there's the ה, read "hay" and pronounced /h/. This stands for Haya, was.
Then there's the ש, read "Shin" and pronounced /sh/. This stands for Shum, There.
In the game the generally accepted rules are: Nun, nothing happens. Gimmel, the player takes the entire pot of pennies. (Afterward all players contribute one penny to the pot.) Hay, the player takes half the pot. Shin, the player places one of his or her own pennies into the pot.