The Spell Book Magazine is an action item that is obtained by logging on to Team Fortress 2 anytime during the Scream Fortress 2013 Halloween event. When equipped, this item allows the player to find and cast Magic spells. These Magic spells are restricted to Helltower, however variables can be changed to enable them on custom Halloween maps.
If it is not equipped, a notification will be displayed allowing you to equip it by pressing J or cancel by pressing K. It will continue to display the notification until you equip it. It will not display the notification unless you are playing on Helltower.