genetics - Functions of the CFTR gene?

I am a senior in high school and I am studying cystic fibrosis.

I don't quite get the function of the CFTR gene as this is my first time dealing with this type of heavy scientific info.

I had searched up its function on a website like this: http://omim.org/entry/602421?search=cystic%20fibrosis&highlight=fibrosi%20cystic

By reading the gene functions section, I learned that CFTR regulate the formation of a chloride channel, changes the regulation of other transport pathways (i.e increase sodium ion absorption in sodium ion absortion). At the same time it also regulate the chloride-coupled bicarbonate receptor. And that is about all I got from that section.

I would greatly appreciate if someone can summarize all the functions of the CFTR gene listed in layman terms (i.e grandma language) and also explain to me why decreased chloride channel leads to thicken mucus or increase sodium ion absorption leads to CF Symptoms. In addition I would also appreciate it if someone can tell me does decreased CFTR gene function also lead to other diseases on top of Cystic fibrosis.

Thanks