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. Typically, players in good guilds can go places and do things that players in poor guilds or no guild can't. This is especially the case at character levels 60-85, where the dungeons become very challenging.
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. Guilds can be a grab bag where you never know what you'll get. Every guild is different.
Finding a guild can be very easy. People often sit in town asking anyone to join their guild because guilds require a minimum number of members to create. However, finding a quality guild with quality members and leadership can be a difficult task. Don't be afraid to shop around. You can join one guild, try it out, then leave and join another guild until you find one you like.