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

This assumes you have the ini 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 ini file, such as hosts.ini. Let's say the hosts.ini file contains the following managed hosts (e.g. the target systems).

server1.example.com
server2.example.com
[linux]
server3.example.com
server4.example.com
[windows]
server5.example.com
server6.example.com

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

ansible all --list-hosts -vvv

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

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

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

Parsed /etc/ansible/hosts.ini inventory source with ini 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