Vigenere Cipher

Why
The Vigenere cipher is important because it gives us a way to more securely encode a message than using monoalphabetic ciphers

What
The Vigenere cipher is a polyalphabetic substitution cipher.

How
The Vigenere cipher uses a key that is a string of length $$l$$. The plaintext message $$m$$ is divided into substrings of length $$m$$ each and then, the message is encoded using the same strategy as the shift cipher

Example 1
Setup:
 * Take the key to be BED

Question: What is the encoded version of PIZZA given the above key?
Answer: RNDBF