A fresh install seeds an example pipeline so you can see how everything looks.
When you're ready to use HireTale for real, click Remove sample data in the right sidebar footer to clear the demo candidates.
Removing sample data also clears anything you added for those demo candidates (a practice interview or selection of a demo candidate counts as sample data).
Your Settings sheet lists are left intact. Just overwrite the sample data (Recruiter, Role, etc) with your own.