The Terraformer is a building that increases the fields on your planet so that you can construct more buildings when your planet is full. For each level of Terraformer, your planet gets 5 additional fields, one of which is taken up by the Terraformer.
Hint: Terraformer levels require progressively more and more energy to build, largely produced by solar satellites. Since the energy requirements for high Terraformer levels approach those required to conduct Graviton Technology research, you can establish a synergy here: once you’ve managed to complete the Graviton Technology research, you can use the energy to build your Terraformer to level 9, resulting in 36 new empty fields for construction. Once you’ve built all the Terraformers you want, the excess energy required for their construction is no longer necessary. You can have an ally destroy the excess solar satellites and recycle the debris for other uses.
Once built, a Terraformer can never be deconstructed.