You don't "create" the "built-in" administrator account. It already exists and is normally hidden. You can enable it..... net user administrator /active:yes
disable it net user administrator /active:no
That account is not typically used for day to day computer uses, there are a few Apps that do not function well or at all, when using that account.
IF you want a new local user account that is also a member of the local administrators group, try this
Cmd.exe (if you are hiding extensions of known types it might simply say Cmd)
Right click it and choose run as administrator
At the admin command prompt type net user JohnSmith /add
then type net localgroup administrators JohnSmith /add
Restart and log in as JohnSmith
NOTE: Obviously it doesn't have to be "JohnSmith". Any Tom, Dick or Sally should work fine (dealers choice).