How do I make a script, where when you spawn you are automatically unFF?

Insert a Spawn and Change the properties to your liking.

On player login remove the "ForceField" instance like this:

game.Players.PlayerAdded:connect(function(p)
    p.Character:connect(function(c) -- On character loaded
        local ff = c:FindFirstChild("ForceField")
        while not ff do wait() end -- While it doesn't exists the game just waits for it to be loaded
        ff:Destroy()
    end)
end)

You do not need to have a script to remove your FF. Inside the spawn, there are properties to set how long your FF is going to last, you can set that to zero and no ff.