This website was valuable for me in my first job. Please note the following article/link:
Polygraph Examination Rights for Clearance Holders
https://news.clearancejobs.com/2025/04/27/polygraph-examination-rights-for-clearance-holders/
This provides the Basics in terms of the various polygraph exams for those looking to get hired and current employees.
Clearancejobs.com also runs an active forum for discussion of security clearance-related topics, including polygraph screening:
https://discuss.clearancejobsblog.com/