@hampton123 When creating a product in APIM, there is an option to toggle requiring a subscription as shown below
This creates a protected product, which requires subscription and a different key that developers can use to call its APIs. If this is not checked, then it is an open product as mentioned in the docs and can be called by developers' existing subscription key.
These open products are not listed in the developer portal as such, but will need to be protected by other authentication mechanisms and policies, as mentioned in the docs.