I am by no means new to geck but i am very new to making quests, i am trying to make a quest like in "The Water of Life" quest when you have to go in a building and kill all the enemies and then report back to the NPC that assigned you the quest.

Killing a Specific Creature
Create new Creature Entry
Begin OnDeath -> Set RandomQuestVariable to RandomQuestVariable + 1

Killing a Specific Creature with a Specific Weapon
Create new Weapon Entry
ObjectEffect -> Begin ScriptEffectUpdate -> -> If MySelf.GetDead -> If MySelf == SpecificCreature -> Set RandomQuestVariable to RandomQuestVariable + 1

Killing a Specific Creature (not added by you) with any weapon
ActorEffect -> Begin ScriptEffectUpdate -> -> If MySelf.GetDead -> If MySelf == SpecificCreature -> Set RandomQuestVariable to RandomQuestVariable + 1
In Quest Script @ stage it calls an Explosion with an Object Script to collect References and add the Above ActorEffect to them.

Quest
In Quest Script -> When RandomQuestVariable reaches Whatever -> Advance Quest Stage, Do Stuff.

Note: If there are multiple creatures just add them to a FormList and check that instead of SpecificCreature.