There's a lot to a full answer as you need to understand the properties of conductors, insulators, electron bonding/affinity etc etc.
In a conductor the electrons are only loosely bound to their host atoms. So if you apply a potential difference (PD) to a conductor the electrons are easily moved along.
In an insulator the electrons are tightly bound to their host atoms, so it takes a large PD to break the bonds, so at small PD's no current flows because no electrons move.
Pure silicon is an insulator which is why it needs doping, and the amount and type of doping determines the type (p or n) and ability to conduct when a PD is applied. Silicon has a valency of 4 so it forms four tight covalent bonds with its neighbours in a silicon crystal.
Doping with phosphorous (valency 5) creates an n-type semiconductor as it creates an excess of electrons. Doping with boron (valency 3) creates a p-type semiconductor as it creates a shortage of electrons.
On their own I'm not sure that p-type and n-type silicon are much use, but when you put them together you get a p-n junction between the two and at equilibrium the electrons from the n-type will flow into the p-type and the holes vice versa, so the n-type will take on a positive charge and the p-type a negative charge.
Connecting a battery to this setup will have differing effects then, depending on which way round you connect it. If you connect the positive to the p-type and the negative to the n-type then electrons from the negative terminal will flow into the positively charged n-type, then in the p-type you can look at it two ways: (a) holes from the positive battery terminal will flow into the negatively charged p-type, or (b) electrons from the p-type will flow into the battery's positive terminal, and so current will flow (and there's more to it than that, but that's basically how it works).
If the battery is connected the other way round then any electrons left in the positively charged n-type, and any holes left in the negatively charged p-type, will be pulled towards the battery and current won't flow.
The Wikipedia articles explain it in more depth and much more clearly than this:
Semiconductor - Wikipedia, the free encyclopedia
p-n junction - Wikipedia, the free encyclopedia
Have another look at what your book says. It's definitely wrong if it describes pure silicon as a semiconductor - it isn't, it must be doped first.