It's important to know up front that when you export an existing pipeline, the exported file only includes data visible in the pipeline view (i.e. What you see when viewing the pipeline). The exported file doesn't include an export of any boxed email threads, tasks, call logs, meeting notes, etc.
If you still want to import the exported file data to a new pipeline, this article will explain how-to in more detail.
You can also duplicate the layout of an existing pipeline by clicking "Create Similar Pipeline" on the left hand sidebar in Gmail: