Tribes are the teams of the game. You can make or join a tribe if you don't want to be alone, which is kind of boring for some. There are many benefits for being in a tribe. They can protect you from enemy tribes and feed you. They can teach you how to make things, like bronze and bread. If you're leader of a tribe you can have your tribemates do jobs like cooking, building, and fighting for you. As long as you can work hard and obey others, a tribe is a great thing to be part of.
To make a tribe, open your tribe menu. There will be a place to create your tribe at the bottom. Type your tribe name in the box next to 'Create Tribe.' Choose a color if you'd like. Click 'create tribe.' Your tribe is now a team on the leaderboard.
You can set stances for other tribes now. If there are any tribes that you trade with or live near them peacefully, set them as 'Ally.' If you have fought with another tribe, have been robbed by another tribe, or was attacked by a member of that tribe set them as 'Enemy.' All others should remain neutral. You can set your tribe's location if you want, but be careful about that if you have enemies on the server.
Now, where will your tribe's base be? Mainland and Megaland are the best, but if you are good at farming and trading you can go somewhere else. You should build a small shed to store food in and begin building a house and maybe a dock.
Now you need members. Use global chat to tell others about your tribe, or just look around a spawning island. Look for people you have played with before, people who can feed and protect themselves, and people who are trustworthy. Don't let newbies join, unless you are patient enough to teach them. Don't let people who are powerful or have a hard time getting along with others join either.
Once you have some people, set them jobs. Give them jobs by what they enjoy doing or are experienced in. Some examples of jobs are farmer, builder, miner, soldier, fisherman, smithy, cook, trader, and lumberjack. Soldiers fight, smithies make tools, cooks make and cook food, traders import materials found on other islands and trade with others tribes, etc. You should also set rules for your tribe, like 1. No eating from the storehouse without permisson 2. Work hard or you will be kicked out of the tribe 3. Don't kill without order unless it's self-defense 4. No killing, stealing, or burning tribe buildings.
These are the basics of running a tribe. I wish you luck in your adventures.