Select Num Lock from Key drop-down list.

If you don't want to toggle Num Lock at all, select Never radio button.
Select Only when I double-click this key if you want to turn Num Lock on only by double-clicking the key.
You can make I Hate This Key to turn Num Lock on when you holding the key for some time. Select Only when I hold this key for some time radio button to enable this behavior.
If you want Num Lock key to work as usual, select Always radio button.

If you want to get a feedback about the Num Lock is on, select Beep on Lock toggle check box. You will hear a beep every time Num Lock goes on.

Clear Lock in on at startup check box if you want to make sure that Num Lock is off when you starting your Windows session.