PYTHON Programming. Please use comments to explain, thank you!

In cryptography, a Caesar cipher, also known as Caesar's cipher, the shift cipher, Caesar's code or Caesar shift, is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet. For example, with a left shift of 3,D would be replaced by A, E would become B, and so on.

Caesar cipher

Encrypt an input string of lowercase letters (plaintext, first input) and prints the result. The other input is the distance value (distance).