In NAV 2013 R2, new company is created from RTC instead of Classic Client or NAV Developer Environment.
1) Login to RTC.
2) Go to Department --> Administration --> IT Administration --> General.
3) Click on Companies.
4) Click New
5) Enter a Company Name and then click OK.
In NAV 2013, new company can only be created from NAV Developer Environment.
In NAV 2009, new company can only be created from NAV Classic Client.