Hi,
This video explains
What is Second Generation Managed Packages?
How to create a Namespace?
How to link a Namespace with DevHub?
Reference:
https://developer.salesforce.com/docs...
https://developer.salesforce.com/docs... (1 GP & 2 GP Comparison)
https://developer.salesforce.com/docs... (Package Ids and Aliases)
https://developer.salesforce.com/docs... (Before You are creating 2 GP Managed Packages)
https://developer.salesforce.com/docs...
https://developer.salesforce.com/docs...