Tools are unlocked once you reach City Center level 5. Your green Move arrow will turn orange and when you click on it you will see new options available.
With the Move option you are able to move your buildings and decoration around in your city.
With the Sell option you are able to sell your buildings for some resources. You can also sell your decorations for Recon Points.
With the Fortify you are able to make some of your buildings stronger against enemy attacks. The Fortify option adds extra defenses to your city, reducing damage taken by certain buildings up to 50%.