How does DF work by describing the Diffie-Hellman (DH) function and the discrete logarithm problem?

Problem

Write an essay answering the following questions.

Question I: What is the purpose of Diffie-Hellman (DF) protocol?

Question II: How does DF work by describing the Diffie-Hellman (DH) function and the discrete logarithm problem?

Question III: What is the main difference between RSA and Diffie-Hellman protocol?