With the "subscription" product type, you can sell access to any extensions that operate with ACL.
The basic scenario is that you can sell access to the category of articles that are meant to be visible only to the particular Joomla user group.
You can, for example, have the "subscribers" user group in Joomla. Only users within this user group can see the articles in this category.
You can set the subscription product in DJ-Catalog2 and sell access for 1 month. Once the user purchases this product, he will automatically be assigned to the "subscribers" user group. After a month user will be removed from the "subscribers" user group and will lose access to the category of articles with this user group permissions.
Following this scenario, you can sell subscription access to any 3rd party extensions that operate with Joomla! ACL.
When editing a subscription-type product, you can specify how many days it is valid; you can also select the user group to which the user will be assigned after the subscription purchase.
If someone purchases a subscription, he gets access to a specific section - for example, the subscribers section where a single user may have access to certain places on the site (e.g., articles).