Joining a clan adds new interesting elements to the game. You can join a clan or create your own starting at level 100. To find a clan, click on the clan icon in the lobby. Read the clan description carefully before applying for a clan: some have requirements for members or a preferred language of communication.
There are several benefits to joining a clan, including the chance to earn valuable rewards, combat gear, and experience as a reward for battles with titans.
Also, a clan is an opportunity to socialize with other active players who can answer questions about the game or give advice.