Patrols are a new way to use your Heroes to help your Alliance. Every day, you can send your Heroes out on gathering missions. If successful, they'll return with Alliance Gems, and Patrol Points, which upgrades your Alliance's Patrol Crate. Once the Patrol Crate opens, every member of the Alliance will receive rewards based on the level of the Patrol Crate.
Note that some Patrols require specific Heroes or types of Heroes, and even after completed, all Heroes have a cooldown timer to prevent using them multiple times in the same day. Heroes used on a Patrol are locked, and cannot be used in other modes until they return from Patrol. Use your best available Heroes, because it's possible to fail a Patrol!
You can also Rush a patrol, for a nominal gold fee, if you don't want to wait. Rushing a Patrol for one of your Alliance members will instantly grant them the rewards, and you'll receive Alliance Gems for your efforts!