The process for making maple syrup is time consuming and directly affected by the weather. Warm sunny days and frosty nights are perfect for sap flow. To begin, maple trees (there are many types) are tapped with a spile and a bucket is hung to collect the sap. Once enough sap is obtained, it is poured into an evaporator and heated until the sugar content is about 65%. Sap is colourless and, as it boils, it becomes more amber in colour. This colouring determines what grade the syrup is - lighter is not sweet and too dark is only used for baking. Medium amber is best and is what can be found on the grocery shelf. Larger producers will have the trees linked up by tubing that flow into one central container to minimize collecting times. In the days before modern technology, sap was poured into large pots and boiled over an open fire.
Since I'm no expert, this is a just a watered down version of the syrup process but for a more detailed and scientific explanation visit Canadian Maple Syrup where you can also read about the history of maple syrup as well as some interesting facts.
I've used maple syrup in cookies and it lends a lovely sutble maple flavour to the finished product. It can also be used to flavour frostings and glazes. Due to its production process, maple syrup is expensive and rightfully so. It is a reflection of the Canadian spirit where something so simple can be transformed into something truly wonderful.