Ceaser cipher

How on earth can one do this???

@kingdecimo take a look @ this repository to get some ideas
Repository Here

i did part of the cs50 course, where i had to write a cesears cipher in C. Here is my solution: https://github.com/stetim94/cs50/tree/master/pset2

Also, edx has the cs50 course (where i solved this problem), you can just audit the course free, maybe you can watch videos on that page for inspiration