To manually share individual records with specific people or group of people on a case by case basis, users can use public groups, roles, or users. Public groups are collections of users, roles, or other groups that can be used to share access to records. Roles define the level of access that users have to their organization's data based on their position in the hierarchy. Users are individual people who log in to Salesforce and have access to records based on their profile, role, and sharing settings.