Ansible is just the automation engine on its own, so it needs instructions detailing all the processes I wish to automate.

If you need to deploy hundreds of server or client nodes in parallel, maybe on-premises or in the cloud, and you need to configure each and every single one of them, what do you do? How do you do it?

Infrastructure is configured declaratively ('infrastructure as code'), which, especially in combination with the management of configuration files in git repositories, enables very reliable deployment ...

Many server automation and orchestration solutions, like Puppet and Chef, rely on a mixture of solution-specific coding, Web UIs, and command-line tools to make the magic happen. Ansible is different.