How to use ConfirmFormBase to confirm the action of another form?

I have a form that allows users to upload a CSV file. Upon submit, I would like to show a confirmation form (“Are you sure you want to import this file?”).

However, the Drupal 8 examples for ConfirmFormBase seem to only focus on building the confirmation form without actually showing how one gets to that form from another form.

Can someone provide an example of a regular form that then works in conjunction with a confirmation form?