Every major cloud provider like AWS or Google Cloud provide their own solutions for infrastructure as code (cloud formation, cloud deployment management). As far as I am aware IBM used to have its own solution but now all I see is on Terraform.
That observation seems correct, IBM Cloud settled on Terraform to provide automation for deploying resources.
You need to set up the IBM Cloud provider for Terraform, configure and then you can deploy resources. Details on the different resources and how to specify them can be found in the IBM Cloud Provider for Terraform docs.