There are many actions in Humankind that allow you to gather resources or spread your sphere of influence across the map. One of these ways is to ransack a tile. You must have a unit in the area in order to select this command and it can a few turns to complete.
With the unit nearby and selected, click the ransack option in the regiment tab. This will highlight tiles you can ransack and you just have to click on the tile to select it.
Ransacking has your unit pillage and loot the tile. This can be done and inhabited tiles on the map such as Encampments and Districts. Doing so will reward the player with resources such as money, food, or science and leave the space destroyed.
Related: How to increase Influence in Humankind
In the Neolithic Era and Ancient Era, you will typically be ransacking Sanctuaries to gather resources. As both your empire the empires of your neighbors grow, you can eventually ransack their tiles. This is of course if the diplomatic relations with you and that empire allow this.
Ransacking will take a set number of turns before it is completed. This is influenced by the fortification level of the tile being ransacked and the combat strength of the army attacking it. Upon completion, the tile will be destroyed and the ransacking player will be awarded the resources.
For more information on Humankind, check out How to gain Era Stars in Humankind on Pro Game Guides.