This tab allows you to create new civilization and assign them bonuses. The only two fields that really matter are the following:
Technology Tree Here each civilization has an effect that mostly disables the common technologies they don't have access to. It can also be used to add some civilization bonuses like discounts, free technologies, etc.
Team bonus This is the effect of the civilization team bonus that will be applied to the allies.
Resources
Another interesting part of this tab is that it stores the resources the game uses. These go from the actual food, wood, etc. to other elements like the food production of farms, the heal speed of Berserkers and many others that control several aspects of the game.