AES: Changing plaintext to state Can someone explain this to me? 
For example how M chanes to 0c?

Changing plaintext to state:
This question has nothing to do with AES; instead, it has to do with an encoding that someone picked for this example (and the fact that you have questions about it indicates that it wasn't a great choice by whoever came up with the example).

The encoding is simple; we translate the letters 'A' through 'Z' to the integers 0 to 25, which is in hexidecimal the values 00 through 1A.

M is the 12th letter after A, and hence it is translated into the integer 12, which is 0C in hex.