a - You find ingame the good npcId.
b - You create the new template. Many solutions :
you create a query with good values directly;
you copy the line concerning the npc from npc.sql, and paste to custom_npc.sql if you got such table. Then activate custom_npc.sql feature.
you copy the line concerning the npc from npc.sql, edit the existing template changing the id and paste the original template back. Then you edit the modified template according to your values.
c - You spawn your crap ingame (//spawn crappy_mob_id).
Then to add skills, 2 solutions :
you edit npcskills.sql directly, adding skills at hand (need good skillId and level).
you edit ingame shift+clicking on the mob, you should have a "skills" tab if you don't use a crappy IL pack (many IL packs got this feature now).
PS : if you use postIL/reworked IL stuff, you have to add an AI aswell. Depending of the AI, mobs will use more or less their skills. Without AI, your mob will be stuck as it will misses important infos (mainly, isMove).