(1) OpAmps Tutorial - What is an Operational Amplifier? - EEVblog, 2014apr06, 1,733,493 views
https://www.google.com/search?q=opamp+tutorial&sxsrf=ALeKk03DZDNaXb20a4fDaO2M0kgHd2Z1nA:1604204829222&source=lnms&tbm=vid&sa=X&ved=2ahUKEwjOh_jXwODsAhXJad4KHWaHATIQ_AUoAnoECBUQBA&biw=1725&bih=863

(2) Operational Amplifier Basics - Electronics Tutorial
https://www.electronics-tutorials.ws/opamp/opamp_1.html

(3) Introduction to Operational Amplifier: Characteristics of Ideal Op-Amp - All About Electronics
https://www.youtube.com/watch?v=kiiA6WTCQn0