After conquering Yhilin, you have to actually run the country. Thankfully, you've been spared from dealing with the details of the budget, but you have some amount of money that you can spend on projects of your choice. Unlike your usual investments, the costs are not denominated in ProN: instead, you allocate the necessary percentage of the available money to a task. It appears that this will be multi-stage process - you'll be able to assign funds while you are in Yhilin and then see the results when you return from missions outside.