Holding key issue help?

If your going to use Keydown() then I recommend you use a LocalScript since it a lot easier to access the Player/Character using local script.

Player = game.Players.LocalPlayer
Mouse = Player:GetMouse()

TurnD = false
Mouse.KeyDown:connect(function(key)-- Parameter
    if key:lower()=="f" then--This checks if the lowercase letter "f" has been clicked" if it has it continues the script
   TurnD = not TurnD-- Changes the TurnD to false and true.It works like this: It check value/boolean if its false it turns it true if its true it turns it false.
print(TurnD)
while TurnD == true do--This checks if TurnD is true if it is then it starts the while true loop.
--Code
wait(1)  
if TurnD == false then-- If TurnD is false then it breaks the loop
break
end
        end
    end
end)