Help Me To UnderStand This Code Line

if (PawnWillClickMe->IsOverlappingActor(ActorThatWillAct))

{

    OpenDoor(DeltaTime);

    DoorOpenLast = GetWorld()->GetTimeSeconds();

}

else

{

    if (GetWorld()->GetTimeSeconds() - DoorOpenLast > DoorCloseDelay)

    {

        CloseDoor(DeltaTime);

    }

}

}

Mainly This Code Line

(GetWorld()->GetTimeSeconds() - DoorOpenLast > DoorCloseDelay)

That code is being ran in Tick so will be called every frame. When the player steps out of the volume DoorOpenLast will stop being updated.

Say the player exited the volume at 5 seconds since the game began.

(GetWorld()->GetTimeSeconds() - DoorOpenLast > DoorCloseDelay)

In half a second increments and assuming DoorCloseDelay is 3, that code would be doing

5.0 - 5.0 > 3.0 | 0.0 > 3.0 -> false
5.5 - 5.0 > 3.0 | 0.5 > 3.0 -> false
6.0 - 5.0 > 3.0 | 1.0 > 3.0 -> false
6.5 - 5.0 > 3.0 | 1.5 > 3.0 -> false
7.0 - 5.0 > 3.0 | 2.0 > 3.0 -> false
7.5 - 5.0 > 3.0 | 2.5 > 3.0 -> false
8.0 - 5.0 > 3.0 | 3.0 > 3.0 -> false
8.5 - 5.0 > 3.0 | 3.5 > 3.0 -> true

From
GetWorld()->GetTimeSeconds() - DoorOpenLast > DoorCloseDelay

[ GetWorld()->GetTimeSeconds() ]
This Will Increment Second Untill The Value is True?

That function returns the amount of time since the game began, so yes.