Once you have all buildings, you may now proceed with advancing to the next stage of civilization—the Stone Age. Upgrading the Town Center and civilization provides you with several benefits—like a higher yield of experience, higher hitpoints against attackers, and a larger storage capacity for Gold and Food.
Growing and strengthening your civilization may seem like an extremely tough job so if you may require some guidance on what step to take next, you may tap on the Wise Man icon which you can find at the top left corner of the screen. As soon as you are able to complete goals, the Wise Man icon will be glowing and will offer you a reward of Crowns.