Ansible is the most popular network automation tool. It is agentless, meaning you don't install software on managed devices. Ansible connects via SSH or API.
Inventory. Lists your devices and groups them logically. Switches, routers, firewalls each in their group.
Playbooks. YAML files describing what you want to accomplish. Human-readable and version-controllable.
Modules. Built-in functions for network vendors. Cisco IOS, Juniper, Arista, Palo Alto all have specific modules.
Tasks. Individual actions within a playbook. Each task calls a module with parameters.