How do can I substitute PlayerAdded so that the script loops?

It think this is what you mean. if you want a script to loop when a player is added, just do this:

game:GetService('Players').PlayerAdded:Connect(function(player)
    while true do
        -- the script you want to be looped in here
        wait(num) -- Replace "num" with the amount of time in-between each loop
    end
end

EDIT Try this script

function OnNewPlayer()
    --put what you want to happen to the game AFTER the player are added here
end

--put what you want to happen before the player is added here

game:GetService('Players').PlayerAdded:Connect(OnNewPlayer)  

EDIT #2 If you just want a script to loop forever, try this here:

while true do
    -- put script here
    wait(num) -- Replace "num" with the amount of time in-between each loop
end