Polarimetry is the key to understanding chiral molecules in terms of optical activity.
This video goes behind the scenes of the polarimeter to help you understand what plane polarized light has to do with chiral molecules.
Part 1 (of 3) in this mini series explains + D and – L, dextrorotatory and levorotatory, and their (lack of) relationship to R and S designations.
(Watch on YouTube: Optics 1. Click CC for video transcription.)