A permission set group streamlines permissions assignment and management. Use a permission set group to bundle permission sets together based on user job functions.
Resource:
Permission Set Groups - https://help.salesforce.com/articleView?id=perm_set_groups.htm&type=5
Define the default access level for an object’s records with organization-wide sharing settings. Organization-wide sharing settings can be set separately for custom objects and many standard objects, and you can set different levels of access for internal and external users.
For most objects, or...
In this lesson I introduce you to Roles and the Role Hierarchy.
Resource:
Create a User Role https://help.salesforce.com/articleView?id=admin_roles.htm&type=5
In this lesson, I demonstrate how to add new roles and edit existing ones. I always advise that you record your current Role Hierarchy via a screen capture or print out before making changes to it.