Basics
Satellite dishes provide television programming and pay-per-view content to your home. They sometimes appear similar to cable TV services and the content they provide is very similar, but the means by which that content gets to you is much different. It starts with the dish itself, which captures the broadcast signals and sends them through the cable into your converter box and from there into the TV. The presence of the dish itself forms part of the reason why satellite TV works the way it does.
Normal TV Signals
Standard TV signals are broadcast from the TV station directly to the antenna in your home. This works fine, provided the station is within a reasonable distance. The farther you go, however, the more the curve of the earth becomes a factor. The broadcast signals travel in a straight line, which can be affected when the earth starts to bend away from it. That's partly why a viewer in San Francisco can't get TV signals from Detroit (not without paying a cable company for the privilege, at least).
Triangulation
One way around this problem is to use triangulation: beam the signal to a separate location and then beam it from that location back down to your home. A spot in orbit --- a satellite --- makes the best method of doing this, because it eliminates the curve of the earth from the equation. The station sends the signal directly up to the satellite, which then broadcasts it directly down to the dish in your home. It can thus reach a huge number of homes very easily, while providing a clear and sharp signal to subscribers.
Synchronization
In order for the satellite to work most effectively, it needs to attain geosynchronous orbit over the earth. That means it moves at the same speed as the earth's orbit, keeping it "hovering" in the same spot over the planet. Geosynchronous orbit provides a steady location relative to the ground, both to beam the signal up to the satellite and for the dishes in people's homes to pick up the satellite's broadcasts. That's why your satellite dish needs to be pointing at a precise location in the sky: it's aimed at the geosynchronous orbit of the satellite itself.
Programming
As for specific channels, the satellite companies themselves broker deals with the various stations to broadcast their content. They pay a fee to ABC, TNT, the Home Shopping Network, HBO, etc. for the rights to their shows. That fee is then passed on to the consumer as part of the satellite service's monthly rate. Satellite companies can thus offer programming packages, with more expensive packages containing a larger number of channels, instead of simply beaming every possible channel into every subscriber's home.
Tags: your home, beam signal, broadcast signals, curve earth, dish itself