They're what you use before you do the final formatting in a Word processor like MS Word.
They both break up chapters into scenes. yWriter has lots of fields and sections to capture data about the scene/book. Scrivener has some but allows you to create your own. Both are good.
For my first few novels, I was having trouble storing ideas or calendar dates or subplots I wanted to work in. These writing programs solve that problem. I wrote a couple books on yWriter and decided to give Scrivener a try, so I'm using that now.
Some writing programs do your plotting for you (as I understand it). That takes the fun out of writing a novel for me.
yWriter
http://spacejock.com/yWriter5.html
Scrivener
http://literatureandlatte.com/
Oh, yeah, and both are written by Brits, so the spelling isn't American.
But maybe this isn't what you want. Maybe you want something that will be more of a nanny program. Don't know what to suggest for that.
on edit
Write It Now looks pretty good.
http://www.amazon.com/WriteItNow-4/dp/B002PRIT0O/ref=sr_1_4?s=software&ie=UTF8&qid=1363220316&sr=1-4&keywords=novel+writing