An alliance is where a group of players come together to chat, help each other out, fulfil big alliance orders, and strive to become the mightiest alliance on the leaderboard.

You can find the alliance features by hitting the "alliance"-button in the menu:

There you can join an alliance, view the profiles of other players and even start a private chat with them. From the middle tab, you can also contribute to the alliance orders, once the leaders of your alliance started one.

You can find the alliance chat by hitting the "speech bubble" icon in the menu: