example_creature_quest.lua

local NpcId = 123
local QuestId = 123

local function OnQuestAccept(event, player, creature, quest)
    if (quest:GetId() == QuestId) then
        creature:SendUnitSay("You have accepted a quest!", 0)
    end
end

local function OnQuestReward(event, player, creature, quest) // Same effect as OnQuestComplete
    if (quest:GetId() == QuestId) then
        creature:SendUnitSay("You have completed a quest!", 0)
    end
end

RegisterCreatureEvent(NpcId, 31, OnQuestAccept)
RegisterCreatureEvent(NpcId, 34, OnQuestReward)