When you bring a magnet close to another metal object such as a nail, the nail will be attracted towards it. This power of attraction is created by lines of force which surround the magnet. They cannot be seen, but if you place a thin sheet of paper over a magnet, and scatter iron filings on the upper side of the paper, the filings will fall into place according to the lines of force. They will reveal what is known as a magnetic field.
Most of the filings on the paper will be attracted to the two ends of the magnet. These ends are the magnet’s poles. The earth itself is like a giant magnet, with its opposite ends at the North and South Poles. This is why the metal needle of a compass will swing round until it is in line with the earth’s magnetic field and points towards the North Pole.