How does a tower crane can start its function by itself standing?

This is what I had encountered before 2015 where I was a construction surveyor at Masbate Gold project, according to CEO: Mr, Ryan Rush to level the 3 temporary saddles for the laying of a crane boom balancer prior for its installation. It turns-out a question in my mind on how to assembled its body. And i found out that they used an aide of a mobile crane to erect the balancer and its first 3 modules of its body as a first moved.Then they fixed on its base. Then, from that,the said tower start lifting the portal frame and inserting its 4th module and then the crane itself pulling it up  the portal frame upright.By the processed I noticed finally that the crane is ready for its purposed of lifting the shell plates for the installation of 4 units CIL tanks,each 16meters dia. & its height.