Touch the black, or negative, tip of the discharge pen to the capacitor's cathode.

This is the lead that you previously identified with the minus symbol on the side of the capacitor.

Touch the red, or positive, tip of the discharge pen to the other lead, the capacitor's anode.

Do NOT connect the positive and negative terminals of the capacitor together with standard wire, screwdrivers or wrenches as this will damage the capacitor and could cause bodily harm to the user.