using part of a theme in another theme

This won’t be an easy or “some clicks” way to archive your goal.

In theory, you will need these things to make the portfolio function work:

  1. function registers portfolio post type.
  2. Template file for that post type.
  3. Custom metabox for that post type. – For adding custom fields.
  4. Javascript file for handing animations, events… for displaying portfolio at front-end. (optional).
  5. Additional CSS.
  6. Theme options. (optional)

For the number 3, you can add your metabox via functions.php. Or you can using CMB2 to easily add metabox to your custom post type. If you prefer plugin, Advanced Custom Fields or Metabox.io are good choices.