Clans allow players to unite under one coat of arms and form a strategic alliance that benefits all its members. Being in a Clan allows players to develop rapidly, stay protected from enemy attacks, and take part in specific tournaments that are only available to Clan members.
At the beginning of the game, you will be invited to join a computer-generated clan. These Clans don't have a leader or a capital. They are designed to familiarize you with the basic mechanics of Clans and are very limited in terms of the range of benefits they offer, compared to player-created Clans.
To join a player-created Clan or create your own, you must leave your current Clan first. Click on Leave Clan in the Clan information tab.
Next, to create a Clan, click the "Create a Clan" button. You will be prompted to select a name for your new Clan, a three-letter Clan tag, and an emblem. Click on Create Clan to confirm. Creating a Clan costs 7.5K Gold.  You can then select whether your Clan will be private, request-only, or open for everyone to join, and you can also select your Clan's primary language.
To join a user-created Clan, click the "Find a Clan" button, which will take you to your Kingdom's Clan rankings. Here, you can browse Clans and join one or submit an application to do so.