So far you've created cloud resources by clicking through a console. That works for a single server, but it doesn't scale: it is slow, hard to repeat and easy to get wrong. Infrastructure as Code (IaC) solves this by describing your networks, servers and databases in text files that a tool turns into real resources. Because the definition is code, you can keep it in Git, review it, test it and rebuild the same environment as many times as you need.
You'll start with the core ideas, including declarative and imperative approaches, then build real infrastructure with Terraform, which works across cloud providers, and AWS CloudFormation, the AWS-native option. You'll finish with Ansible, which configures what runs on your servers once they exist. Watch the videos in order, then move on to Containers.
The idea behind IaC, why teams use it, and how it makes infrastructure repeatable.
Start from scratch with Terraform: the workflow, configuration files and core concepts.
Use Terraform to create infrastructure on AWS from code.
Build and manage AWS resources with CloudFormation templates and stacks.
Install and configure Ansible, then use it to set up and manage your servers.