You need:
A server with DB acess
Navicat, HeidiSQL or SQLyog(This guide is made in HeidiSQL)
1. step
Open you're DB launcher( HeidiSQL etc) and find the table named "playercreateinfo"
2. step
In this guide we will create an undead palla, Okay now log into you're WoW acc and create and undead, Then log out. Okey now go to the table "playercreateinfo" again and scroll down untill you reach the bottom.
3. step
Just look on the the tab that has the number 433( Just write the same as I do there)
4. step
Now go to the table named "characters " and find the undead you created(Just search it's name) and find the tab named class and change that to 2, Then just restart the server and you should have a undead paladin
Enjoy
PS:This is my first guide