Playbooks are Ansible's configuration, deployment, and orchestration language. They can describe a policy you want your remote systems to enforce, or a set of steps in a general IT process.
At a basic level, playbooks can be used to manage configurations of and deployments to remote machines. At a more advanced level, they can sequence multi-tier rollouts involving rolling updates, and can delegate actions to other hosts, interacting with monitoring servers and load balancers along the way.
While there's a lot of information here, there's no need to learn everything at once. You can start small and pick up more features over time as you need them.
You should look at `Example Playbooks <https://github.com/ansible/ansible-examples>`_ while reading along with the playbook documentation. These illustrate best practices as well as how to put many of the various concepts together.
