Add Local Users.
||Run [Server Manager] and Open [Tools] - [Computer Management].
||Right-Click [Users] under the [Local Users and Groups] on the left pane and select [New User].
||Input UserName and Password for a new user and click [Create] button. Other intems are optional to set.
||After creating normally, New user is shown on the list like follows.
||If you'd like to set administrative priviledge to the new user, Right-click the user and open [Properties].
||Move to [Member of] tab and click [Add] button.
||Specify [Administrators] group like follows.
||Make sure [Administrators] group is added on the list and click [OK] button to finish settings.
Windows Server 2016 : Initial Settings