Create Looker Sankey Diagram

[Ashton_Du]

Hi there,
I’d like to create a Sankey Diagram to show flow. Data will be like page views. Users will be directed to 1st page, and then to other pages.

Data:
timestamp, user_id, page_name

How should I properly create Sankey diagram? I found very limited sources online.
Need to know:
1). Is it necessary to prepare data in certain form? If yes, what form does it have to be?
2). How to prepare in LookML

Thanks!