It's a pleasure, ndtvideas123.
Book Designer is a very powerful program, but can be a bit cranky at times. I strongly suggest that you download HarryT's Book Designer Tutorial - see the first post in this thread:
https://www.mobileread.com/forums/showthread.php?t=10313
It is very useful in guiding you through how to make a book.
And if you ever decide to tackle text files (eg many of those from Project Gutenberg) then paste the text file into a Doc, save it, then run Stingo's Macro:
https://www.mobileread.com/forums/showthread.php?t=8793
This will remove all those annoying end-of-line breaks and give you a nice reflowing text. Then put the file into BD.
And do ask again if you have any more queries.
I got my Reader in May 2007, and I knew NOTHING AT ALL about all this. I got a lot of help from people on this forum. Now I'm really quite proficient, thanks to all the advice and a lot of practice.