You should run terraform init after you start coding a new Terraform project and before you run terraform plan for the first time. This command will initialize the working directory by downloading the required providers and modules, creating the initial state file, and performing other necessary tasks. References = :
Initialize a Terraform Project

The concept of infrastructure as code (IaC) is to define and manage infrastructure using code, rather than manual processes or GUI tools. A script that contains a series of public cloud CLI commands is an example of IaC, because it uses code to provision resources into a public cloud. The other options are not examples of IaC, because they involve manual or interactive actions, such as running curl commands, sending REST requests, or entering commands into a console. Reference = [Introduction to Infrastructure as Code with Terraform] and [Infrastructure as Code]

The public Terraform Module Registry automatically exposes all the information about published modules, including required input variables, optional input variables and default values, and outputs. This helps users to understand how to use and configure the modules.

Terraform configuration can import modules from various sources, not only from the public registry. Modules can be sourced from local file paths, Git repositories, HTTP URLs, Mercurial repositories, S3 buckets, and GCS buckets. Terraform supports a number of common conventions and syntaxes for specifying module sources, as documented in the [Module Sources] page.
References = [Module Sources]

Before using a remote backend in Terraform, it is mandatory to run terraform init. This command initializes a Terraform working directory, which includes configuring the backend. If a remote backend is specified, terraform init will set up the working directory to use it, including copying any existing state to the remote backend if necessary.
Reference = This principle is a fundamental part of working with Terraform and its backends, as outlined in general Terraform documentation and best practices. The specific HashiCorp Terraform Associate (003) study materials in the provided files did not include direct references to this information.