What EXACTLY is TANTRA and how does it differ from Bhagwad Geeta teachings?

What is tantric Vidya, giving sacrifice and do people who do tantra get moksha? How does it differ from Gita teachings? Does Vishnu/Krishna accept it? Why and why not? Is Krishna worshipped in Tantra? I don’t suppose it’s Satvik then why is Krishna or Vishnu worshipped in it? Why is Shiva? Why is Hanuman? Krishna said he lives in all living beings so why is sacrifice of an animal okay in tantra? How is different from Satvik and what is better? (I AM NOT INTO TANTRA OR SACRIFICE OF ANY ANIMAL, it’s just a respectful decision and curiosity because I would love to know about what exactly is it and where does Krishna stand in it and anything and everything in detail! )