[Help] Refresher

[Illustria]

Hey, im working up a source i need some refreshers though, in regards to npc placement. Theres a few things i need explained in the source itself.

NPCID < --- Im guessing is just a random somewhat chronological ordered npc identification
NPCType < --- Is the npc reference for where in the source it finds the coding to state what that npc does.
SubType < ---- Im guessing the npc's icon?

Basically i wanna add some npcs that arent quite implemented into the game. As well can help me later on down the road when i add monsters.