How does our Constitution change?
As you learned in your text, there are generally three ways. A formal amendment can be approved by Congress and ratified by the legislatures of 3/4 of the states. Sometimes, the meaning just evolves - as the President's role in war changed during the Cold War. The most common way, though, is through judicial interpretation, especially by the U.S. Supreme Court.
The First Amendment to the Constitution begins "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof..." What exactly does that mean? The first part (the "establishment clause") originally meant only that Congress couldn't establish an official national religion. Many American colonists left England, where the church and state were one entity, and wanted to avoid letting that happen again.
Over the years, though, the Supreme Court has take a somewhat broader view, and the issue has gotten more complicated. If a public school begins each day with students bowing their heads and praying, is that an "establishment of religion?" The Court has said yes. In December, can the city have a Christmas tree in front of City Hall? The court has said yes - that's a fairly generic holiday decoration, despite the name. What about a nativity scene? The court has said no, that's a celebration of a specific event from the Gospel of Luke in the Christian Bible.
The court has said at various times, that Harris County couldn't display a Bible in front of its courthouse, but that the State Capitol in Austin can keep a monument with the Ten Commandments on it. As I said, it's complicated.
The second part, the "free exercise clause," has had similar lines drawn. Yes, practitioners of certain indigenous American religions can use peyote, even though it's a controlled substance. No, you can't practice human sacrifice, even if your religion honestly believes in it.
Last year, the Supreme Court issued an interesting, controversial ruling in a case called Burwell v. Hobby Lobby. The issue: Can a closely held company (a family business, for example) refuse to pay for certain birth control measures as part of its insurance for its employees, as is required by the Affordable Care Act (Obamacare), if doing so violates the religious faith of the company owners?