What Exactly Happens In Cystic Fibrosis?

Hi there.

So, my uncle (married to my mom's sister) died of Cystic Fibrosis before I was born, six months after he married my aunt. So, I knew that he had died, but I didn't know what he died of until very recently. So, I've started to wonder more about what this actually is. What exacly goes wrong? What symptoms happen? Of course, I've heard about this in science class, but I've never really known the ins and outs and I've started to wonder. Can anyone help me out?

By the way, my aunt has now been living without her husband for twenty-five years. She's never remarried, and she's doing fine. She knows he's waiting for her in heaven.