The Essential primordial beej mantra is “om”, it's the mantra from which all another mantras ended up born. Each individual beej mantra has a certain god or goddess connected with them. The types of beej mantras are— Yog beej mantra, Tejo beej mantra, Shanti beej mantra, and Raksha beej mantra. https://www.youtube.com/watch?v=7yoEpl90KUg