The player community puts the MM in MMORPG. While there are a great many things you can conceivably do all by yourself, there are times where you will be forced into dealing with *gasp* other people. Running instances, buying items off the auction house, communicating in General Chat, or just getting ganked on a PvP server are just a few ways players can mingle.
You can send messages to any character who is on the same server and a part of the same faction as you are. Most communication is performed by using a Slash Command. For example, /say will cause you to Say whatever you type next so the people around you will notice it.
You may bump into other PCs while adventuring. If you do, it's often important to try to determine their motives. On a PvP server, a member of the opposite faction might try to kill you. On the other hand, most people of your own faction are probably just trying to quest or farm. With perhaps the exception of the PvP encounter, try to use common courtesy when dealing with them. Your reputation in the player community matters, and you might be able to help each other.
One driving purpose for player interaction is trading. While adventuring, a player may stumble upon a very good item that they cannot use themselves. But that person needs money. It seems like a no-brainer that with other players around, it would be wise to see if anyone else is interested in purchasing their phat lewtz.
Finding a player to buy your item isn't always easy. Shouting in every zone is tedious and will make people resent you. As an alternative, the global Trade channel allows a player to make buy and sell requests to anyone else in a city. All uninterested players can easily leave the channel.
An even more common recourse is to use the Auction House. Every major city will have a place to list your items for a period of up to 24 hours. Interested players can make bids, and at the end of the auction, the item is sold to the highest bidder and the money is mailed to you with a small fee taken out. If the item doesn't sell, the item is mailed to you instead.
Unfortunately, the Auction House does not have the ability to sell everything. Enchanters, in particular, are known for constantly hawking their skills in the Trade channel because they don't general sell actual items. Players also often need to resort to the Trade channel to find players that have the tradeskill and particular recipe or pattern they need.
Out of necessity or convenience, you will sometimes team up with other people. This might be to run an instance or complete an elite quest, or it might just be to kill a quest boss that both of you were after so you both get credit. If you enter into a party, try to be clear about what everyone expects from the group, as it is not always obvious.
To create a party between you and a single other person, target them, right-click on their Character Portrait, and select Invite. This will give them a message offering the chance to join a group with you. If they accept, their portrait and health will appear under your's down the left side of the screen. At this point, you would be the Group Leader -- with a crown over your portrait to mark it. Only the group leader can invite new people, and that player also has a few other controls over the group such as how loot is distributed. If you decide to leave a group, right-click on your own portrait and choose Disband.
When a group of players want to band together for some sort of common purpose, they usually form a guild. Guilds exist for many different reason; some are elite teams of dragonslayers while others are merely a collection of friends.
Guilds have their own chat channel, and the officers of the guild have a private channel of their own. When not performing a guild-wide activity, (if the guild does any large activities,) the guild chat channel is often filled with banter or requests for help to finish a dungeon or to craft an item.
Every guild is very different. Some have a very centralized structure, while others have no structure at all. Some are strict about who they admit, while others blindly invite passers-by. If you are interested in joining a guild, it pays to know a little about who they are first.
Raids are essentially super-groups that can have up to 40 players in them. Depending on what the raid is attempting, there may be a limit on the number of players that can participate. For example, Karazhan is a 10-player dungeon. Though more players can be invited to the raid, only 10 can actually enter the zone.
Raids truly are groups on steroids, though. Every player in a raid typically needs a very well-defined role. There needs to be a leader and expectations on goals and loot distribution. Most raids exist as a means to attempt dungeons specifically designed for raiding, but there are also a handful of Outdoor Bosses and sometimes players just want to have a means of incorporating more than 5 players to a group. Also, PvP players will often make raids for attacking the other faction.
It should be noted, however, that any player in a raid will not be able to receive credit for any quests that are not marked as raid quests, and once a group has been converted into a raid, it will remain a raid until it is disbanded.
Player-versus-player content takes many different forms, but the general theme of PvP is summed up in its name: players fighting each other. This most often takes the form of Horde vs Alliance struggles, but there can be PvP within a faction in the case of dueling or arenas.
Many players engaging in PvP will be ruthless and use all manners of cheap and dirty tricks, while others have more of a code of conduct or prefer to organize with allied players for more coordinated efforts. Here are the different styles of PvP:
Motives for PvP vary. What was originally just a chance to wage war on alleged opponents has come to include elements for ranking and loot reward systems. While most players PvP for the sake of PvP, there are some who enter battlegrounds or arenas because they perceive it as an easy way to upgrade their equipment for minimal effort.
Some players prefer to speak rather than type under certain circumstances. For some, it is simply a more convenient way to interact, while for others it is a means of getting messages across expediently. Players involved in raiding or group PvP in particular are known for using programs like Ventrillo or Teamspeak. In October 2007 (v2.3), Blizzard added voice chat as a native aspect of the game. A few general tips about using Voice Chat:
World of Warcraft exists well beyond the game that millions log into each night. There are fansites, information resources, web communities, and even a few comics around the Internet. Discussion Boards tend to be among the most popular overall, with the most notable being Blizzard's own, often refered to as the Official Boards.
See WoW on the Internet for more information.