How do I add a rotating brick and it stays running?

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You could make a script and put this in it then put the script into the brick

while wait() do script.Parent.CFrame = script.Parent.CFrame * CFrame.fromEulerAnglesXYZ(0,0.1,0) end

I suggest you to look Here and Here That should teach you how to make it keep spinning(Anyways here is a script)

while true do
Part.CFrame = Part.CFrame.new(1, 1, 1)
wait(0.1)
end