Case law, also called "jurisprudence", is law that is based on court decisions rather than law based on legislation. It stems from cases heard and decided in courts and tribunals.
In Canada, the law requires that judges take note of the previous rulings of other judges in higher courts in their province or territory, and the Supreme Court of Canada on the same issue. This is called "precedent" or stare decisis in Latin. This helps judges apply the law consistently throughout the Canadian court system.
When looking for case law, it is best to start with secondary sources - legal experts will identify leading (important) cases and provide analysis, doing some of the work for you. Encyclopedias and legal treatises are a good place to find leading cases.