The Situation:
* You have a Lord of D and a Dragon on the battlefield.
* Your opponent casts Lightning Vortex.
Lightning Vortex's Effect:
Lightning Vortex deals 3 damage to each creature.
Lord of D's Effect:
Lord of D's ability gives all other Dragons you control +1/+1 and trample.
The Outcome:
* Your Dragon will be dealt 3 damage by Lightning Vortex.
* Lord of D will not be affected by Lightning Vortex. It's not a creature, so it doesn't get damaged by spells that target creatures.
The Question of Trample:
* If your Dragon has enough power to deal lethal damage to your opponent after the Lightning Vortex damage, the trample ability will let the excess damage go through to your opponent.
Key Points:
* Spells that target creatures only affect creatures.
* Lord of D is an enchantment, not a creature.
* Trample only applies if the creature has enough power to deal lethal damage to your opponent *after* other damage is dealt.
Let me know if you have any more Magic: The Gathering scenarios you'd like to analyze!