Time for action - exiting
I love the story of the infamous 19th century circus entrepreneur P. T. Barnum (the Barnum in "Barnum & Bailey"). Old P.T. believed in moving the rubes (the public) along if possible. He is said to have posted a sign reading "The Way to the Egress" and people would rush to see the Egress only to find themselves outside the tent and having to pay again to get back in. Egress, of course, is just another word for "exit."
Click on Exit on the File menu in Celtx and you'll find yourself outside also as Celtx closes down. Being more on your side than circus and carnival hucksters, Celtx makes sure you saved your last changes. Basically, it works exactly the same as the Close, Close Tab (as the last tab is closed), and Close Window menu selections. This completes the File menu, so let's go on to the Edit menu.