This is part of publishing/exposing your API Proxies.
In (very) short, API Products represent the API proxies you're publishing, the environments they're available on, access controls.. Developers are the consumers of your APIs, and Apps are the entity that associates a developer to an API product/s and provides credentials to them.
I suggest taking a look at the first module of our API Jam and run through the labs. This will take you through the process end to end of creating your first API Proxy with Apigee and then publishing them and consuming them as well so you can understand this end to end lifecycle. You can also then appreciate some more of the finer details enabled with this approach such as quotas via products, restricting resources, etc.
LinkedIn
Twitter
