Terraform is a powerful tool for creating and managing greenfield infrastructure, as well as managing existing resources from popular infrastructure providers like cloud-based databases. It allows users to migrate manually created infrastructure into its workflow, enabling them to manage the entire lifecycle of their project with Terraform's configuration language and workflow. Users can import existing resources into a Terraform project's state using the terraform import command, allowing them to start managing those resources without destroying or recreating them. This process requires creating additional configuration to match the state created by the import process.