Quarters is one of those games that when you start losing, you keep losing. It's a very simple game and can be played with as few as three people, or as many as you can comfortably fit around a table.
A quarter (or similarly sized coin1)
Two shot glasses (you can use one if you don't mind trying to not swallow a quarter)
Your favourite type of beer
Everyone sits around a table, and the empty shot glass is placed in the middle of the table2. The second shot glass is filled with the beer, and kept off to the side. The first player takes the quarter and attempts to bounce it off the table and into the empty shot glass. If they miss, play continues to the left. If it goes in, they get to choose one of the other players, who then drinks the full shot of beer. The drinker then refills the glass and play continues from the left of the last person to bounce.
Usually, one person will end up getting the hang of it, and everyone else will be taking shots of beer. One technique that seems to give the most control over the quarter is to bounce the face against the table.
A good reason to play a drinking game of this type is if you feel like having a beer, but don't actually have any good beer. By only having shot-sized glasses, and by drinking those relatively quickly, you don't have to dwell on the low quality of the beer you have on hand. This is in contrast to most other drinking games, in which the players want to be inebriated, but don't actually enjoy the taste of beer.
Just like any other activity in which drinking is involved, care should be taken to avoid driving or operating any kind of heavy machinery during or after the game.