When you're in a town or outpost, the District menu appears in the upper left corner of your screen. When a large number of people enter the same location, additional Districts may appear to keep towns and outposts from getting overcrowded. When meeting friends, be sure to specify which District you are in so they can find you easily. No matter which District you are in, you can always whisper to a specific player or get in touch with your guildmates or alliance, but your global chat will only go out to the other players in your town and District.
Guild Wars lets you play with anyone, anywhere, anytime. While your Guild Wars account is specific to the country you live in, you can meet and adventure with players from other countries using International Districts. For example, if you normally play in the American region, and you have a friend in the Korean region, the two of you can meet in the International District of any town and form a party together. Use the drop-down menu in the upper left of the screen to get there.