Can somehow explain me the difference in these products?
This is not an exhaustive answer, but hopefully it'll point you in the right direction...
App Connect is for building integrations (flows) with various data sources. Could be databases, cloud services like GSuite or Salesforce, or even HTTP endpoints. Those flows could be triggered by events in one of those systems or by an API. You can also do things like turn a database schema into an API. You get the idea.
API Connect is for API governance, security, and socialization. In more concrete terms, it gives you tools for things like: adding authentication and/or authorization to all APIs, bundling APIs together, enforcing rate limits or quotas, providing a portal for sharing/selling your APIs with others, and so on.
You can create APIs using App Connect and stop there--it's usable/invokable without API Connect in the picture. API Connect provides enforcement policies to give you more flexibility in how you call that API and/or give others the ability to invoke the API. The two products complement each other, but an API management product would be required in order to manage and govern the APIs created by App Connect.
In terms of licensing, there are multiple available options. You can purchase the products as standalone software packages that you install and maintain yourself (see IBM Cloud Pak for Integration) or you can leverage the IBM-managed versions that IBM provides via IBM Cloud.
More information is available: