Explanation
This is the command that can add existing resources into Terraform state, by matching them with the corresponding configuration blocks in your files.

You can configure a backend in your Terraform code before initializing it. Initializing a backend will store the state file remotely and enable features like locking and workspaces.
References = [Terraform Backends]

* It lets you version, reuse, and share infrastructure configuration as code files, which can be stored in a source control system and integrated with your CI/CD pipeline.
* It reduces risk of operator error by automating repetitive tasks and ensuring consistency across
* environments. IaC does not necessarily provision resources at a lower cost, secure your credentials, or prevent manual modifications to your resources - these depend on other factors such as your cloud provider, your security practices, and your access policies.

The two steps that are required to provision new infrastructure in the Terraform workflow are init and apply. The terraform init command initializes a working directory containing Terraform configuration files. It downloads and installs the provider plugins that are needed for the configuration, and prepares the backend for storing the state. The terraform apply command applies the changes required to reach the desired state of the configuration, as described by the resource definitions in the configuration files. It shows a plan of the proposed changes and asks for confirmation before making any changes to the infrastructure.
References = [The Core Terraform Workflow], [Initialize a Terraform working directory with init], [Apply Terraform Configuration with apply]

This is not true, as modules can be either public or private, depending on your needs and preferences. You can use the Terraform Registry to publish and consume public modules, or use Terraform Cloud or Terraform Enterprise to host and manage private modules.