Yet another noob asking for help scripting

[Repus32]

////////////////////////////
// Run first time starting map
void OnStart()
{
SetPlayerLampOil(0);

}
////////////////////////////
// Run when entering map
void OnEnter()
{
PlayMusic("09_amb_safe", true, 0.9, 5, 0, true);

AddUseItemCallback("", "Key_1", "Door_1", "UsedKeyOnDoor", true);

void UsedKeyOnDoor(string &in asItem, string &in asEntity)
{
SetSwingDoorLocked(Door_1, false, true);
PlaySoundAtEntity("", "unlock_door.snt", "Door_1", 0.0f, false);
RemoveItem(Key_1);
}
}
////////////////////////////
// Run when leaving map
void OnLeave()
{

}

ERROR: expected ( at 16,8!

Could someone please help me fix this?

[Your Computer]

You're not supposed to define a function within another function (i.e. take UsedKeyOnDoor out of OnEnter).

[Repus32]

Many thanks upon you, good sir. Is there a tutorial page for this out there somewhere?

[Your Computer]

Is there a tutorial page for this out there somewhere?

For what exactly? Defining a function? How to handle errors? Understanding scripting in general?