Tibia is strongly based on the community and one's relations with others. Guilds strengthens one's relations with others in the world.
The guilds could be organized guilds made to bring wealth to their members (eg. Mercenarys, Black Dragon), to help other players (eg. Tenth Legion (Danera /Danera Academy ), Loremasters, Rising Dragons (Secura/Amera/Antica)), or just as a family or group of very good friends (eg. Castlings, Henceforth Family, Crimson Chaos).

To join a guild, first go to the guilds page and select your world. Then, scroll down to and select the world in which the invited character resides. Afterwards, find the guild and select the view button on the right and enter the guilds page; once in the guild page, select the 'Join Guild' button. As a sidenote, you must be logged into your account to join the guild.

To create a guild you need a premium account and also 4 vice-leaders with premium account too. Go to the guilds page, choose your world and scroll down to the bottom and click the Found Guild button.

Note that only one character per premium account can be a guild leader or vice-leader.
Sidenote: The guilds leader can decide to rent a guildhall. This is a great opportunity to rent a room, even if you are a free account player.

New features

In the winter update of 2014 new features have been added to the Guild system.