https://www.chabad.org/therebbe/article_cdo/aid/154179/jewish/Sefiras-HaOmer.htm
https://www.chabad.org/library/article_cdo/aid/363609/jewish/The-Principles-of-Kabbalah.htm
https://www.chabad.org/library/article_cdo/aid/361868/jewish/The-Key-to-Kabbalah.htm
https://www.learnchassidus.com/documents/Making Ourselves Shine.pdf