A guild is typically an in-game association of player characters.
Guilds are formed to make grouping and raiding easier and more
rewarding, as well as to create a social atmosphere in which to enjoy
the game.
Banking guilds are also used by many individual players as a way to
increase the rather limited bank storage space available in the game.
Background
Guilds offer many benefits including free items, opportunities for
groups, access to trade skill masters, quest items, and readily
available trade skill ingredients through gathering guild members.
You may discover that a guild greatly enhances your gameplay
experience. You can meet friends, share adventures, and find people
to protect you if you fight in faction versus faction combat.
Keep in mind that guilds are run by players and not Blizzard. The
quality of the guild and the guild experience depends entirely on the
players in that guild. Every guild is different.
Starting a Guild
Talk to a guild master NPC in a major city. A charter can be
purchased, and you will need other players to sign the charter before
you can turn it in and start your guild.
Choosing a tabard design costs gold, but the guild can be created
without paying for the tabard design. When you still have the guild
charter, you can change the guild name to something that is not taken.
Guild names are case sensitive, meaning names with different
capitalization may be treated as different names.
Once you begin getting signatures on your charter, focus on getting
the remaining signatures and registering the guild. Signatures can
disappear if you delay, since players are allowed to sign other
charters until yours is turned in.
Benefits
Guilds can provide perks, rewards, social support, easier grouping,
and access to organized dungeon, raid, and battleground activities.
Having a group of people willing to help makes later content easier,
especially when entering high-end instances and raids.
A guild bank lets members exchange items, store supplies, and help
other members with materials or equipment.