Magnets have two poles, a north and a south pole. When you break a magnet, that part will then gain its own north and south poles. While a magnetic monopole in theoretically possible, there is no experimental or observational evidence of it existing.
Magnetism is caused by the parallel alignment of electron spins in Ferromagnetic materials. Each electron spin causes small magnetic domains, which, after being pointed in the same direction, magnetizes the material. A material that is magnetized can align the electron spins in an unmagnetized ferromagnetic material, leading that material to be magnetized.
The Earth behaves as a large bar magnet, but the geographic North pole is the magnetic South pole.