Basics In order to join or create a guild, you must first be at level 30, and join either Britra or Deva. If you join Britra, you can only join Britra guilds, and the same goes for Deva. In order to join a guild you might also need to agree to certain rules.
If you want to create a guild it will cost 100,000 tra. Guild creation is taken care of by the NPC Volkan Landman in the western corner of Andarasa. It is free to join an existing guild, unless the guild master charges for admission.
Currently, there is no real reason to join or create a guild. Each guild exists for different reasons. Some guilds were made to be the strongest, and others were made to simply be a guild of friends from the real world.
Guilds provide no basic benefits to members other than membership. The only thing membership gets you is the ability to wear a cape with the guild's logo. Any other benefits of joining a guild are based on the guild master's and guild members' decisions and rules, so think carefully before joining a guild.