While it is possible to make a piece of iron magnetic by stroking it in one direction with a strong magnet, the resulting magnet tends to be rather weak. To create a powerful magnet, the easiest and most effective method is to build an electromagnet---a relatively easy task.
Using the wire strippers, strip a small amount of insulation from the ends of the copper wire.
Working carefully and methodically, wrap the copper wire around the nail. Wrap only one layer of wire, and do not double back and wind in the opposite direction. When the core is completely covered with wire, stop winding. The direction of the magnetic field produced by the voltage is determined by the direction of the wire rotation. Opposite-directional windings will result in the magnetic fields cancelling each other out.
When the wire completely covers the core, connect the two stripped ends to the two terminals of the DC source. The voltage flowing through the wire will produce a magnetic field.
Make sure the core is made of iron. A non-magnetic core will not create a powerful magnet. This will not work with AC power. You must use a DC source such as a battery. To increase magnet strength, you can increase the size of the core, the diameter of the wire, the number of wire turns, or the voltage of the DC source.