Users can have different privileges in the system: Admin, Recruiter, Hiring manager, Reader, ..., and more can be added in the future. The best place to know which permissions are granted is under "Company settings" > "Company users", where an Access rights table can be found after the table with users.
There are dozens of different permissions in the system, and they can differ from company to company. (At the time of writing it is not possible to change the access rights in the table though. Also permissions aren't yet translated to other languages):
These are system-wide permissions. Being a member of recruitment team for a specific position can give extra access to the position in question.
Persons, which approve job requisitions, are not necessarily users in the system. They receive one-time access on per job requisition basis.
See also an article about user management.