Knowledge pertaining to the magic arts can be transmitted in several ways.
The most commonly used mode of transmission of the knowledge pertaining to the magic arts is word of mouth, through face to face interactions, typically between magic masters and their students.
The second most commonly used mode of transmission of the knowledge pertaining to the magic arts is the written word: typically through the textbooks written on magic and the paranormal.
We can’t also rule out the possibility of the knowledge pertaining to the magic arts being nowadays transmitted through tools of technology, such as email. If, for instance, a given magic master goes to the Gmail account login page at www.gmail.com and jots an email to his or her student giving instructions on how to perform a certain magic feat, transmission of knowledge would have taken place. Of course, the magic master in question will want to be assured about the security of the medium being used in this way, because the last thing he or she would want is having the instructions pertaining to magic being sent to student ending up being intercepted. But then again, even if someone else intercepts the instructions, it would be hard to make sense of them without the necessary background information to contextualize them.