Download HeidiSQL (search on Google). Go into ascent. Click on the section for what ID you need (Creature_names for creatures or items for items). in the search bar at the top type in the name of the display ID you need. If you need Illidan's diplay ID, search for Illidan Stormrage, if you need Warglaives of Azeroth, search for it. Scroll over until you see the section for Display ID, and your done. You can use these IDs for creating custom weapons, custom NPCs, etc.
Thanks for listening
-Ledz