Activating the Workflows feature made the Approval - SharePoint 2010 workflow and the others you see in the list above available to be used with lists and libraries. If the Approval workflow does not appear in the list, then the Workflows feature has not been activated for the site collection.
Note that you can change the workflow settings before starting it, including who the task is assigned to as well as adding additional users or groups. These settings are the same as the ones you can configure when you add the workflow to the library. The setting you choose when you add it to the list or library become the default settings when you start the workflow.