Action plugins act in conjunction with modules to execute the actions required by playbook tasks. They usually execute automatically in the background doing prerequisite work before modules execute.
The ‘normal’ action plugin is used for modules that do not already have an action plugin.
You can enable a custom action plugin by either dropping it into the
action_plugins directory adjacent to your play, inside a role, or by putting it in one of the action plugin directory sources configured in ansible.cfg.
Action plugin are executed by default when an associated module is used; no action is required.
You cannot list action plugins directly, they show up as their counterpart modules:
ansible-doc -l to see the list of available modules.
ansible-doc <name> to see specific documentation and examples, this should note if the module has a corresponding action plugin.