MKDIRSYSTEM StatementWindows/Unix

A statement that creates a new directory.

Syntax: MKDIR pathspec
MKDIR "abc"

mkdir "C:\BAS\RAPIDQ\help2\1234" -  without last slash
mkdir "C:\BAS\RAPIDQ\help2\1234\" -  with last slash,All variants are working

MKDIR will not rewrite a directory if one already exists, if no path is specified, the directory is created in the current working directory. Also don't use string variables with $DEFINE, use an actual string variable.
$DEFINE TheDrive "C:"
$DEFINE TheFolder "\~~tmpFolder"
$DEFINE TheDrive_Folder "C:\~~tmpFolder"
'MKDIR TheDrive + TheFolder    'doesn't work
'MKDIR TheFolder                      'doesn't work
'MKDIR TheDrive_Folder            'no go