How do I get a list of folders and sub folders without the files?

Try this:

dir /s /b /o:n /ad > f.txt

 Displays a list of files and subdirectories in a directory.

 DIR [ drive:][path][filename] [/A[[:]attributes]] [/B] [/C] [/D] [/L] [/N]
  [/O[[:]sortorder]] [/P] [/Q] [/R] [/S] [/T[[:]timefield]] [/W] [/X] [/4]

  [drive:][path][filename]
          Specifies drive, directory, and/or files to list.

  /A          Displays files with specified attributes.
  attributes   D  Directories                R  Read-only files
           H  Hidden files               A  Files ready for archiving
           S  System files               I  Not content indexed files
           L  Reparse Points             -  Prefix meaning not

just set type of desired file attribute, in your case /A:D (directory)

dir /s/b/o:n/A:D > f.txt