Pretty much. On your iOS device, you’d use the App Store app, and so it is on the Mac. When you want to buy something, you enter in your iTunes ID and password and, boom—it’s purchased. The app downloads automatically, too, and what you bought is automatically placed in the Dock. (You can move it out later, if you want.)

The Mac App Store is open to pretty much every country that lets you buy stuff from Apple—90 in all. It seems like most of the international exclusion issues involving iTunes media do not exist on the Mac App Store, so you should be able to buy in your own country and get the same stuff you’d get in the U.S.