Hi, this is my first guide (Its pretty simple).
Its to find the Display ID of an NPC (can work for items too) if you dont have accese to a DB.
Ok start by going to wowhead.com and type in an NPC/Item name, i am going to use the NPC called Ox:
Next go right click anywhere and go to View Source
Next we type Control + F to bring up a little search button type in display and go next
The ID is the number next to Display ID
So for example Ox's Display ID is 6854.