After a personal account has been linked to an organization account, the person will show up on the Employee list of the Organization > Account > Members > where the assignment of an access role is requested.
The persons that are linked to an organization DO NOT HAVE ACCESS to any information of an ‘organization account’ UNLESS they have been assigned the correct ‘access role’ from the Administrator.
By default, the Administrator is the person that created the ‘organization account' via his personal account.
In the given example, Oscar Mouse will have the access role ‘administrator’ of the ‘organization’ as he set it up as the owner. That means that he has full access to his ‘organization account’ and consequently only he can assign different access roles to new linked ‘personal accounts’ once they have been added. Please read everything about the access rights of the different roles here: Access roles and their rights in organizations