You can't export your entire contacts folder as a vCard (vcf) file.  To
export one contact, open that contact and click File>Save As.  Select "vCard
Files (.vfc)" in the "Save as type" drop-down.  Give it a name.  Click OK.
If you want a vcf containing all your contacts for exporting to another
program (i.e., not Outlook), you can use Notepad or a command prompt COPY or
APPEND to join them together.

Outlook's import will import vCard files containing single contacts only.
If the file contains more than one, only the first will be imported.