Hi,
In Acymailing->Subscription forms you get a choice over four kinds of subscription forms. When you create one of the type Header, Footer or Popup they are also listed here.
When you choos Module you will be redirected to Joomla->Extensions->Modules, where you can create a Joomla module of the type Acymailing subscription form. This one is not listed in Acymailing->Subscription forms because it is located in the Joomla module manager. You can treat it like any other Joomla module.