1. Do you haveto be a wiccan or a pagan to cast spells
No. Magick is a thing that any and every person can do. Obviously calling upon a Pagan deity might not work without being at least a little pagan yourself, but there are magicians of every faith. It's also possible to be of no faith or to even be Atheist and perform magick.
2. Does everyone need a book of shadows
No. While there have always been books of magical lore, the Book of Shadows started with Gerald Gardner and the founding of Wicca. While this obviously means that non-Wiccans aren't required to have one, Wicca itself is very flexible in terms of specific practices and so even some Wiccans do not have a Book of Shadows. Many non-Wiccans have since adopted the practice of keeping a Book of Shadows as well, though it is still a predominantly Neo Pagan thing.
3. What do you put in the book of shadows ( plz could u answer this question page by page
There is unfortunately no set page-by-page answer to give you. While sometimes a tradition of Wicca (specific branch, like Lutheran Christians and Episcopal Christians, for example) or a coven will have a group Book of Shadows that each member will copy from, people are encouraged to personalize their Book of Shadows by changing and adding things.
There are a lot of different things that can go into a Book of Shadows, but they all fall into three main groupings;
Spiritual Lore
Rules, creation myths, and other "normal" religious stuff like you think of for a Bible.
Useful Magical/Spiritual Information
Calendar and how to celebrate holidays, tables of correspondences for colors and numbers and most other things, charts detailing what things are associated with what gods, etc.
Spells & Rituals
While most agree that a book which is nothing but spells and rituals is NOT a real Book of Shadows (it's a book of spells, oddly enough), important or frequently used spells and rituals are often included.
In general it should be full of whatever you think is most important in your magick and spiritual development.
There's advantages and disadvantages to making a book of shadows. It takes a lot of time to put together, especially if you do it the old fashioned way, by hand. And its easy to go overboard and put more than you need. However, writing it yourself helps you remember, and it's easier to have all your info in one place rather than searching through a bunch of books and websites.
"It takes a lot of time to put together, especially if you do it the old fashioned way, by hand. And its easy to go overboard and put more than you need."
Yeah, but that's also part of the beauty of it. By having to put so much effort into writing each thing in your Book, it really makes you question whether or not you actually feel like it's that important. When I last worked on my BoS there were several things where after a few hours of trying to write them without screwing them up somehow, I realized that whatever it was simply wasn't worth it. You end up having a greater appreciation for what you really believe and what you really value.
Many magicians, myself included, will make a BoS and keep it for a few years and add new things to the back and note things in the margins. Then, after those few years have passed, we'll decommission the old BoS and make a brand new one based off of the old one. We'll take the things added to the back and write them in the order most appropriate and we'll make the changes noted in the margins, and we'll throw out anything we no longer use or find relevant. That way our Book will truly be suited to us even as we evolve.