So you know you love Bordeaux, but why is it that when you go to Napa, there isn't a Bordeaux grape being served anywhere? And why, when you go to a French restaurant, can you never find a good French Merlot on the menu? Out of luck? Au contraire.
In short, the Old World (Europe, in general) has a system of naming its wines far different from that used in the New World (America, South Africa, Argentina, New Zealand, to name but a few). By identifying a wine based on its region, wine drinkers of the Old World are able to predict (more or less) the wine's characteristics. What to do, though, when you're used to being told what varietal you'll be enjoying?
By simply knowing which grapes grow in which region, you'll know which wine you should order in order to satisfy your craving for Chardonnay, for example. That said, since varietals are grown in different regions, styles will vary depending on the region. But at least you'll know to order a red Burgundy when you have a hankering for a Pinot, and not be shocked and disappointed that you can't find your favorite red on the menu.
(To get you started)
In Bordeaux, the classic varietals (which tend to be blended), are:
Red: Cabernet Sauvignon, Merlot, Cabernet Franc
White: Semillon, Sauvignon Blanc
Burgundy is for Pinot Noir and Chardonnay fans, while the appellation of Chateauneuf-du-Pape (part of the Cotes du Rhone region in France) yields wines made of Grenache, Syrah, Mourvedre, and several others. What's important to remember is that a Cotes du Rhone promises to be a powerful, thick, often spicy wine.
Check out the Winecyclopedia for more info on several other regions in the world!