Whipping Boys, and Girls

I am interested in politics, but still not as aware as I could or should be on its nuances.

One thing I really need to find out about this 'Whip' lark.

It has cropped up before, but I really took notice today during a piece about stem cell research, when the reported explained that this was one of the rare cases when MPs can vote with their conscience, and is not 'told' how to.

In a democracy, when you essentially give your proxy to your MP to act on you will in Parliament, by my current understanding, at least on how it sounds, I simply have to question what the pint of my mandate to this person is worth.