How do you start a Book of Shadows?

You don't need to use a quill. Some people write their book of shadows on the computer.
First you can add some basic information to your Bos.
And here is a small tip to begin.
Grab 7 sheets of paper;
on the first you write Deity concepts
on the segundo you write Tools,altars,jewelry
on the third rituals
on the fourth beliefs
on the fifth rules
on the sixth symbols and runes
on the seventh spells

So you can add information on each page and that will form your Book of Shadows. This is just a tip so it's entirely up to you what you do :)

A Book Of Shadows is your personal book on your experiences of your Craft. In it you write how you're feeling before and after doing a spell or a ritual. How you're going to do your alter and whether any changes occur to it (excluding the natural changes as you go through each monthly holiday) and also reminders as to what you use for each main event and why.
I'm completely different from deathRoman13 - my BoS is mine and mine alone, and that's what i put my own spells in or my favourties i have found and copied. My experiences with Tarot or gems or scrying etc.
What you've called the Grimoire (which i call my second) is where i copy all the main rituals for each event in case i forget what to do and need some prompting, all the different meaning for symbols and runes, other people's spells i have tried or like etc.

To be honest no one can actually tell you how to use your book of shadows as it is yours. All we can tell you is how we use ours. It is your choice and responsibilty to find out what is best for you and your craft :)

Could buy one at a new age store
Or make one ur self
U put in it
Power thoughts
Spells
Power dreams
Stuff that's inportant to u