In the lower-left corner of the screen, under the movement joystick, you will see a button labeled "AUTO." If you tap this button, your Exile will begin automatically collecting all accessible Resources in your current location. This means that they will pick up all Resources on the ground, and harvest Resources if you have the appropriate tool. For example, if you have a Stone Axe, your Exile will use it to cut down trees to get Pine Logs. You will NOT collect Items in containers or from defeated enemies.
Your Exile will continue auto collecting until all of the slots in your Inventory are full. If you have no Inventory slots left, but the stacks of Resources in those Slots are not full, your Exile will continue to automatically collect the types of Resources that can fit in those stacks, while ignoring the types of Resources that there is no room for.
You cannot begin auto collecting if there are any dangerous creatures in the location you're at. Dangerous creatures are those that will attack you if you get too close, and are marked as orange circles on the mini-map in the upper right of the screen. Defeat all enemies at the location to make auto collection possible.
While auto-collect is active, you'll see a yellow ring highlighting the "AUTO" button. To stop auto collecting, you can tap the button a second time, or interrupt the automatic movement by moving manually with the control stick.