The basic license level comes included as part of your ArcGIS Online subscription. It allows you to share open data and create open data sites and pages that can integrate, and leverage data driven visualizations and apps created with ArcGIS.
The premium license level provides added functionality and tools that make your community engagement efforts easier, including tools for creating and managing initiatives and initiative teams, an event management system, and dashboards for monitoring feedback and progress. It also provides community members with identity accounts that allow them to create a community profile to provide feedback, sign up to attend events, follow initiatives, and receive relevant updates. ArcGIS Hub administrators can also leverage included initiative templates and tools to help them manage internal and external collaboration and participation.