Few questions on how to write a book?

You have to do your own research and ask people who've had ghostly experiences to relate those to you first hand, and allow you to use them in your book. It's always a good idea to get something on paper giving you permission to use a story, because if you published a successful book of anecdotes and someone who was cooperative changed their mind, you could have a court case to fight. The best way of getting people to take part is to place ads asking for people who've had ghostly experiences and who would be willing to tell you for the purpose of publishing a book, to get in touch with you. It is, of course, possible for you to use accounts you've heard second hand, without naming names, without getting any permission, so long as you absolutely use no names or anything which would identify a person. That's because most experiences aren't exclusive to one person.

This is either the work of a troll or the most naïve question posted so far this year.

No, you can't just steal other people's work.

Yes, you have to ask in writing for permission to include their experiences in your book. You should get advice from a reputable lawyer who specializes in creative rights legislation. I think you should retain one, because negotiating contracts with those people who experienced hauntings may take a long time and some squabbling.

You're actually serious about this o.o

You will need to have a legally binding contract--something non-lawyers probably can't do well enough--to obtain the rights to the stories for the purpose you will use them.

If you are hoping to use other people's stories in your book then you must get their permission in writing first. (unfortunately, verbal agreements mean nothing in court any more.) If their experiences have already been in print, then you need to investigate each one for copyright protections and attempt to obtain permission to use their copyrighted materials, either free or via some compensation plan. Any part that you don't get the releases in writing to use will make the entire book illegal and can result in it costing you!.

If you do advertise for people to tell your their ghostly experiences you will certainly need to have a very clear agreement with them about the use you are intending to put them to. Also, how will you know they have not simply made them up, or, worse, taken them from copyright sources.

As long as you don't use their names, and they haven't filed for a copyright on their stories you are free to just steal them and print them as your own.

I'm not sure you need a contract. I mean, if the stories aren't copyrighted you wouldn't have to like pay them 15% of the profits. It is best that you ask them though and make sure they're okay with their stories being on a book. I would also change the names of the people involved since people also don't like their info being on display.
Hope this helps

if you wish to use other peoples work you need permission and most will demand to be paid a royalty.
To obtain permission contact the publisher of the text that you saw the story in or contact the authors agent. You can write to authors c/o their agent or publisher. In writing - allways in writing and signed.