You are looking in the wrong area, but it isn't really your fault. The books aren't organized in the best manner. The main rules for the Realms of Battle are in the Core rules book. Malign Sorcery then has an expanded list of spells that can be used within each realm of battle. Near the end of Malign Sorcery are the rules for choosing a Realm of Origin for your army. This where you gain access to the Artifacts of the Realms.