The Gold Saucer is split into seven different areas, called "Squares" - the Battle Square, the Chocobo Square, the Event Square, the Ghost Square, the Round Square (?!), the Speed Square and the Wonder Square. Each square will be covered in more detail below. The entrance and exit to the Gold Saucer is accessed through the Station.

A different monetary unit is used at the Gold Saucer. Instead of the regular Gil, Gold Pieces (GP) are used. GP is needed to play certain games and to use to Save Point at the Station. There are many ways to earn GP - winning the Arcade Games at the Wonder Square, finishing first at the Chocobo Races and so on. However, there is a one-in-sixteen chance that a man will show up at the Station who will exchange 100 Gil for 1 GP.

[Spoiler] You'll be visiting the Gold Saucer twice during the game. The first time is an acquaintance to the place, and if you go to the Wonder Square, Cait Sith will join your party. The second time you'll be looking for a Key to the Temple of the Ancients, and to obtain it, you must fight at the Battle Arena.

The Battle Square

At the Battle Square, one character will fight eight consecutive battles in order to earn Battle Points (BP). Battles cost 10 GP. These BP can be traded for a valuable item - you'll be most interested in the W-Summon Command Materia, and Cloud's Lv4 Limit Break, Omnislash. Be careful - as soon as you leave the Battle Hall, you'll lose all your BP. There is a maximum of 65000BP you can have. After each battle, you'll spin a slot machine - you'll get a certain handicap applied to you when a certain picture appears:

Here's a list of the items you can trade for with your Battle Points (Disc 2 and 3):

[Optional] Once you have Omnislash, a W-Summon Materia, and beaten Ultima Weapon, you'll be able to participate in a Special Battle by talking to the registration lady. The format is exactly the same as before, but you'll be facing tough monsters and bosses instead. Your prize is the Final Attack materia. Should you fail, you'll be able to retry as long as you have the required GP to pay.

The Chocobo Square

If you're raising Chocobos, you'll be spending quite a lot of time in this square. Here, you'll race against other Chocobos, and if you win, you'll earn a ticket which can be exchanged for lots of GP or an item. There are four ranks - C, B, A and S, the best. The rarer items must be obtained while you're in the S Rank.
When racing, you can choose between the Long Race, or the Short Race. Each Long Race is worth 2 points, while the Short Race is worth 1 point. You need 6 points to advance a Rank. And sorry, there are no consolidatory prizes for second or third.

The Event Square

Nothing here, but you'll be visiting the Event Square in the course of the game.

The Ghost Square

You can rest up and buy some items here (All costing some GP, of course). There's also a Turtle's Paradise Flyer by the entrance to the Item Shop - inspect it for later use. Also grab a Megalixir in the Blue Cupboard in the Hotel Room when you stay the night.

The Round Square

For 10 GP you can tour the Gold Saucer via a Gondola. Not much, but some very cool FMVs in the process.

The Speed Square

For 10 GP, you can sit in a rollercoast and fire energy beams at any moving object for points. If you get enough points, you'll get a prize. However, points aren't cumulative, so you need to make the most of your ride. Each time you pressed, the intensity of the beam decreases, so you'll want to fire to short, sharp bursts, allowing the beam to recharge. Once again, shoot anything that moves. The UFO at the end is worth a 1000 points, so make sure you get it. There's a also a yellow boulder at the top of the canyon wall worth 2000 points.
Prizes vary depending on which disk you're on.

The Wonder Square

For a few Gil, you can play the several Arcade Games at the Wonder Square. You'll get GP if you do well, and these can be traded for items with the attendant there.