I realized that "most basic" system is not as basic as it could be
It could be far simpler just for to start:
Player: uses gun from inventory and uses on NPC on screen. (On screen gun from inventory changes to crosshair?).
Game: chacks if he has a [bullet] in inventory, if true:
SFX of a gunshot is played
NPC changes sprite to "dead NPC"
Bullet is removed from inventory
Am I right that this would far easier and possible to implement for a begginer?

It could be far simpler just for to start:
Player: uses gun from inventory and uses on NPC on screen. (On screen gun from inventory changes to crosshair?).
Game: chacks if he has a [bullet] in inventory, if true:
SFX of a gunshot is played
NPC changes sprite to "dead NPC"
Bullet is removed from inventory
Am I right that this would far easier and possible to implement for a begginer?