How would I make a script that only runs when the player is moving?

humanoid has a function called running:

local running = false

game.Workspace.Player.Humanoid.Running:Connect(function(speed) -- define humanoid
    if speed > 0 then
        running = true
	
	 -- code here(but make sure to constantly whether the player is running via the variable)
	
	
    else
        running = false
    end
end)

for ur instance since ur function is already a loop u can do this:

local running = false
local Num = 0

game.Workspace.Player.Humanoid.Running:Connect(function(speed)
    if speed > 0 then
        running = true
    else
        running = false
    end
end)

game:GetService("RunService").RenderStepped:Connect(function()
	if running then
		Num = Num + 1
		
		print(Num)
	end
end)

PS: im not merging the speed function with the renderStepped such that u can use it to check other things but u could also just combine it to loop check the humanoid speed