How can there be ball magnets? I've come across those ball magnets, and I was wondering how it is possible since I was under the assumption that for any magnet, there was a North and a South pole. These magnets are made to be assembled in any way imaginable, which seems to contradict the fact that each magnet has opposed poles. 
Do they really have only two hemispheric poles, which may mean that some shapes will not be possible because of the repulsion of poles of the same polarity?

 A: Yes, all magnets have north and south poles. There is no such thing as a unipolar magnet (a magnetic "monopole"). This is called Gauss's law of magnetic fields.
A: They are probably akin to the earth's magnetic field, which as I'm sure you know only has two magnetic poles.
The thing you have to remember is that they really can't be put into every possible configuration. This would be more obvious if they had clearly marked poles. Because balls all look the same everywhere, you can't tell that the magnetic fields are all lining up. 
A: The balls can only assemble in such a way that they touch each other, approximately, with opposite poles.
That they have poles can be seen below. The picture shows the fields B and H for a uniformly magnetized sphere, which should be a good enough approximation here. The magnetic south pole is where the straight field line enters and the north pole where it leaves the sphere. A compass needle will point to the magnetic south pole. Note that the Earth magnetic North Pole is actually a south pole. Also of course Earth, or its metallic core, are not uniformly magnetized.

A: One must consider the alignment of the atomic plates within the metal. If all positive poles are pointing towards the center of the piece of metal, then the very center point of that piece of metal becomes the positive pole. When all outward facing poles, or plates, in this sphere are negative, then then entire outter surface becomes its negative pole. One can reverse that and bring all of the negatives facing inward which should create a glow if there is enough plates within this piece of metal to allow the sphere to Glow. It is correct to say that all magnets have a North and South Pole, but we assume that they both need to be on the external surface.
