Man-in-the-middle Attack, Certificates and PKI by Christof Paar

I've been watching this series by Christof Paar to better understand the fundamentals of cryptography. Many of the other videos in this series are heavy on the math, to explain the mathematics underlying various algorithms, but this one is very practical for almost everyone, because as a programmer, you will have to deal with certificates at some point.

Why aren't public and private keys enough? Why are certificates necessary? What even is in a certificate?

Lecture 24: Man-in-the-middle Attack, Certificates and PKI by Christof Paar