In Response To 'Re: Re: Calculating point-plane distance'
That book appears to have been $129 when new. Now AbeBooks.com and other fine used book dealers will put a copy in your mailbox for about $10.
I think that would be a excellent introduction for you to using Mathematica for geometry problems and even Mathematica in general and should not be too advanced for you.
Some parts of Mathematica have changed since the book was published, but the underlying mathematics and equations will always remain the same.
If you want a copy you might order one before other readers here snap up all the cheap copies. Having good books that target specific uses of Mathematica seems like an excellent investment.