Here is an example in a graphical view to quickly get familiar with different SharePoint administration roles and level of responsibilities in a Farm hierarchy.
Following table provides detailed information on each role. To learn more, click here.
Server or Farm Level
Farm admins have full control of the farm, and they are able to assign other admins to manage different service applications. By default, they don't have access to individual site content.
Local Server Windows admins
Farm admin added to this group are able to install new applications, Web Parts and features to the global assembly cache. By default, they don't have access to individual site content.
Service App admins
Farm administrator assigns these users to administer service applications. Their role is only scoped at the service application level, and they are not able to access and manage any other service application to which they are not assigned to.
Feature admins are only assigned to specific features of a service application. For example, audiences feature of the User Profile service application.
Site Collection Admin
Site Collection admins have Full Control permission on all Web sites in a site collection, including their content. They also receive e-mail notifications such as site reaching a quota limit.
Site owners for a site have the Full Control permission level on that site only, including its content such libraries, lists, and items. They also receive e-mail notifications for events, such as the pending automatic deletion of inactive sites and requests for site access.