In order to keep all of your vacancies organised and to manage user permissions effectively you can create 'Locations' and 'Departments'. The level of granularity that you apply will depend on the size of your organisation and how finely you want to control user permissions.
Setting user permissions at the Location and Department level will allow you to restrict access to vacancies and applicants accordingly. So for example you may want your Human Resources department to have access to everything but not your Marketing department.
Locations might be high level such as 'Unite Kingdom', 'United States' and 'Asia' or they might be more granular such as 'London', 'Glasgow', 'New York', 'Denver' and 'Dubai'. It's up to you to choose what works best for the size and scale of your organisation.
It's also fine for you to have just one location.
'Departments' are dependant on the structure of your Organisation and typically this might be something like 'Human Resources', 'Accounts', 'Sales', 'Marketing' and 'Customer Service'. You can create as many or as little as you need.