On this Long Beach Chant site, you will find a few videos, but other websites have spent a lot more time (and money) in developing professional online teaching resources:
and the Youtube channel : https://www.youtube.com/c/GregorianChantAcademy
Please start with this excellent 5-minute video:
Do you prefer a private teacher, or to organize a group teaching event, either online or in-person? Angela Maria Rocchio’s International Chant Academy is our recommendation: https://www.chantacademy.com/
… Or you just want to learn the most ancient and meaningful chants of the Gregorian tradition?
This podcast may be what you are looking for : https://www.floriani.org/podcast