Most people think of judicial review in the way that Justice Owen Roberts described it in a 1935 Supreme Court decision:
The Constitution is the supreme law of the land ordained and established by the people. All legislation must conform to the principles it lays down. When an act of Congress is appropriately challenged in the courts as not conforming to the constitutional mandate, the judicial branch of the Government has only one duty — to lay the article of the Constitution which is invoked beside the statute which is challenged and to decide whether the latter squares with the former. All the court does, or can do, is to announce its considered judgment upon the question.
It seems straightforward. A judge takes a law, sets it next to the Constitution, and determines whether the “latter squares with the former.”