Taking care of your Chickens:
In most parts of the world winters are not a big issue. Howerver, once you go north/south of certain latitudes then keeping your chickens going through the winter is a big deal.
Winterizing your Shelter
If you are using an existing shed that has wall cavities(in between the outside siding, and the inside wall) you can fill those up with sawdust, and that helps.
Depending on the size and cold tolerance of your chickens heating can be very important or just a nice add on. If your shelter is small enough and insulated well the heat produced by your chickens might be enough to keep them warm. If this is not the case then it might be necessary to put heating in. A heat lamp can help add warmth to the chickens shelter. The cold tolerance of chickens varies. However, some chickens can be quite happy in -20 celcius.
Butchering all your chickens in the fall
One option of getting your chickens through the winter is to not do it. If you are raising chickens for meat purposes then this is an option worth considering. For instructions on doing this look in the Butchering section of this book.