The Duet is able to power a heated bed up to 18A. This should be well above the requirement for most heated beds.

If your heater has an integrated LED, then the polarity will matter as the LED will not light with reverse polarity. Otherwise, a heater's polarity doesn't matter.

It is recommended to use the included ferrules, by crimping them to the wires before putting the wires in the terminal block.

Do not tin (add solder to) these wires.

Be sure not to twist the terminal block while tightening the screws. It can help to hold the terminal block while tightening.

Check the screws after a few days/weeks of operation to ensure they are still snug.