creating a secret key for the encryption audio file using AES Algorithm ?

i am a begginer at matlab , i am working on my project in which i have to embed audio file with in a particular region of grey scale image. first of all i have to creat a secret key for audio file and then have to encrypt that audio file to ensure its security using AES(Advance Encryption Standard Algorithm).please help me how to creat it or what are the steps to encrypt and decrypt a simple audio file using AES algorithm