This is one of the most important phases of your command. You should always try keep your builders busy as that makes your Base more and more powerful with each Improvement or Building constructed. The build queues will show all construction information regardless of it's type (Building, Improvement, Add-On).
To hire extra workers, tap over the second queue and use the Extra Workforce item this will effectively double your construction capacity for the duration of 24 Hours per used item. Use it wisely as this may greatly boost your Base forwards.
All constructions can be SpeedUp for free at their end depending on your VIP status. Also don't forget to join a large Alliance as Allies can help you out when building stuff around your Base