Constitutional law is a body of law which defines the role, powers, and structure of distinct organisational units within a governmental setup, namely, the executive, the parliament or legislature, and the judiciary; as well as the basic rights of citizens. You may find the info here about the constitutional law, law of writs and jurisdiction of courts in Pakistan.
Constitution is not an ordinary statute made in ordinary legal procedure. It is the creation of a Constitutional Act and therefore the sanctity of a Constitution is much higher than any statute made by the legislature. A Statute is an act to fulfill a particular social, political or economic need and so its efficacy of importance does not endure so long. But a Constitution is made to endure with the avowed purpose to fulfill the aspiration of the people who made it. It is by the people, for the people and a documentation of the cherished good of the people. Constitutions are not conceived and acted in vacuum, and as an instrument of Government. It is always intended the condition and as it is itself conditioned by the circumstance and environment of the community whose activities seek it to regulate. It is never internal and differs from other laws only in respect of general national purpose, it has in view. Constitution, written – unwritten has a philosophy of its own: it is the means of ordering the life of people. This way we should have good understanding of our constitution.