Standard channels are split into six themed groups, called "entertainment mixes". Each one has a number of channels in it. Each one costs £1 per month.
Then you can add on "premium mixes" i.e. movies and sport. These are optional.
Finally you can choose a standard sky box (don't do that), Sky+ (eye opening if you've never had a PVR before), or Sky HD (not great value for money but I'm happy with mine).
A reasonable
full price breakdown is here and
lists of what is in each channel mix is here.
If you want to sign up to the triple play i.e. broadband, TV, and home phone you get discounts. And do it through
quidco too - I got £130 cashback when I took out SkyHD around Christmas. I've been very happy with it (SkyHD+6mixes+no movies or sport + phone + 16meg broadband).