Communities User Licenses

A user license determines the baseline of features that the user can access. Every user must have exactly one user license. You can view the user licenses that your company has purchased to know what you have available to assign to your users.

There are three types of licenses in the community:

1. Customer Community License
• Customer Community Licenses get a basic feature.
• If external users who need access to case objects or knowledge, you can use a customer community license.
•  It includes High Volume Customer Portal, Service Cloud Portal, Authenticated Sites Portal.
• Customer Community Licenses can’t have roles, hence they can’t take advantage of role-based sharing and the sharing set is used for them.
2.  Customer Community Plus
• If your community members need access to below, Then you probably need Customer Community Plus Licenses
•  Reports and dashboards
• Delegated admin
• Content libraries
• Records across accounts
• Salesforce normal sharing rule works for Custom Community Plus.
3.  Partner Community
• If In addition to the above (Customer Community Plus), do your community members also need access to below object, Then you probably need Partner Community Licenses
• Leads and opportunities
• Campaigns
• Salesforce normal sharing rule works for Custom Community Plus

In short, Customer Community Licenses get a basic pass, just like an economy ticket. Customer Community Plus Licenses get more access, like business travelers. Partner Community Licenses get way more access, pretty much like first-class travelers.

Reference: https://trailhead.salesforce.com/content/learn/modules/community_rollout_impl/community_rollout_impl_sharing

https://help.salesforce.com/articleView?id=users_license_types_communities.htm&type=5