The claims define the monopoly in words.
A patent may have many claims, each defining the invention in different words and describing it broad or narrow functional language. A typical claim has the following form:
Preamble ... transitional phrase ... claim elements.
In Canada, claims are most commonly of the form having a brief preamble describing the apparatus or method in terms of its field of use, the transition "comprising", and followed by the claim elements (apparatus elements or process steps) which are like a checklist of the components of the claimed invention.
Claims are sometimes analogized as a series of "fences" surrounding and protecting the valuable invention. The claims define the metes and bounds surrounding the protected invention, much like surveying terminology defines the metes and bounds to a piece of land containing gold. The fences must be clearly defined in order to give the necessary warning. Property which is not owned by the inventor must not be fenced in, otherwise the claim will be invalid as being broader than the invention.
Claims are usually drafted with multiple, dependant claims.
For detailed reading on this topic, please visit- http://pharmaceutical-patents.blogspot.com/2009/11/canadian-patent-law-drafting-claims.html