The feature can be found at the Rally Point. Here you will find four options to gather resources without the disruption of other players or losing units by farming. The options can be unlocked - this requires resources for every option and some time. How many resources can be gathered is primarily defined by the selected option and the carry capacity of the units - each resource has almost the same amount. For example it is not possible to exclusively scavenge for iron. Bonuses like from items and flags also influence the amount of resources gathered.
Activation All options can be active at the same time, but you can't start the same option several times. To start the scavenging you have to select units you want to send away and the gather option (or the premium version, which increases the outcome of the gathering). You can only use the units you owe and are stationed in that village, not supporting units. Before you start the gathering, you can see how many resources you will get and how long it will take until the units are back home. Once you activate one option you can't cancel it anymore and you have to wait until the units are back. You can also see the remaining time. If you're scouted while your units are on scavenging, these units are shows as "not in the village".
Finishing/Returning When the units are back the resources are added to the warehouse. If the warehouse limit is reached the excess resources are wasted. Bonuses like from flags or items increase the amount of resources gathered. You will also receive a report when scavenging units return. The report shows: