First off, Yes, I know Construct is spelled with a "C." You find an appropriate letter K word and I will totally change it.
To Plan or Not to Plan
Okay. You decide to write a book. And you decide you would, at some point, actually like to finish writing said book. There are a few ways to go into such a large project, and writers can be pretty attached to their favorite method (even if they've never tried another).
If you are writing a book for your English project this year, part of the idea is to learn about becoming an author, not just tripping through the dictionary and hoping you end up with something usable. So take a few minutes to ponder the following approaches and decide which works for you...
Your Basic Options
Why Examine the Structure Before You Start?
Oh man. I can hear you now: But Anna, I just want to write! I can't be creative this way! Stephen King lets his stories just unfold, I am sure that will work for me!
Sitting down and flying by the seat of your pants can be awesome. And it is super fun if you just want to write for yourself, or if you have a team of editors at your beck and call, or if you have an established, Stephen King-sized fan base.
But if you are writing a book for high school English this year, or if you have limited time to write, or if you just want to finish the thing, then you need to know your story makes sense. If you want to have readers shout, "Man! That was a ride! Where's the next one?" then, well, you are going to have to examine the structure of your book at some point.
And let me tell you, 100k words in is not a fun place to examine structure.
Shuffling index cards around, adding in new ones, or even trashing cards, is way easier. You will save yourself lots of precious time, but you will still be able to sit down with whatever card you are working on and have a creative good time.
The time you save is not having to edit as much later. If you love deconstructing plots and mercilessly cutting up your work and rearranging it, then go for it. I for one would rather chew on my flip flops.