1. Give a proper tag for your question, example:"cryptography".
2. Have you tried
googling for Vigenere cipher[
^]?
3. Assuming you have googled the question, the top most result of the page should be
this page[
^]. Have you read it?
4. Assuming you have read
this[
^] and still doesn't know how to solve the question,
here[
^]'s the part you should read.
5.
It's your credit, do it yourself. Looks like I've got too much free time on my hand,
here[
^]'s a step by step instruction to solve it (Read the Series Information what you should read a series of 5 post starting from this post).