Because subscriptions and licenses evolve and change frequently, the best place to find information is directly from Microsoft. To learn more about subscriptions and licenses, I recommend reviewing the following resources:
- Compare Microsoft 365 Enterprise Plans: https://www.microsoft.com/en-us/microsoft-365/compare-microsoft-365-enterprise-plans.
- Aaron Dinnage's licensing diagrams will help you understand what services and packages fall into which subscriptions and are frequently updated. I particularly benefited from the Venn diagram model: https://github.com/AaronDinnage/Licensing.
- Matt Wade has created the Periodic Table of Office 365, an excellent visualization of the O365 platform and all its apps and service. This can be found at https://www.jumpto365.com/tables/en.
- Staying current can be a challenge but https://msft365admincenter.com/ has gathered many resources that'll help you...