If you are not familiar dynamic inventory, check out Ansible - Getting Started with Dynamic Inventory.

This assumes you have the yaml plugin in ansible.cfg enabled, like this.

[inventory]
# enable inventory plugins, default: 'host_list', 'script', 'yaml', 'ini'
enable_plugins = host_list, yaml, ini

This also assumes you have defined your inventory in a yaml file, such as hosts.yml. Let's say hosts.yml contains the following managed hosts (e.g. the target systems).

all:
  hosts:
    server1.example.com:
    server2.example.com:
  children:
    linux:
      hosts:
        server3.example.com:
        server4.example.com:
    windows:
      hosts:
        server5.example.com:
        server6.example.com:

The ansible command with the --list-hosts and -vvv flags can be used to determine if the yaml plugin is being used.

ansible all --list-hosts -vvv

If you get something like this, this suggests you did not define yaml in ansible.cfg properly.

[WARNING]: Unable to parse /etc/ansible/hosts.yml as an inventory source

If the following is returned, the host_list plugin is being used.

Parsed /etc/ansible/hosts.yml inventory source with yaml plugin

Something like this should be returned.

  hosts (6):
    server1.example.com
    server2.example.com
    server3.example.com
    server4.example.com
    server5.example.com
    server6.example.com

Or, the ansible-inventory --list command can be used.

ansible-inventory --list

Or, the ansible-inventory --graph command can be used.

ansible-inventory --graph