Structure of book chapters
I assume you were approached by one of the main authors, rather than an editor. They can answer your question as they know something about what they want the book to be. You might even be able to get a draft of another chapter if the project is in progress. But there is too much variability for a general answer here. Perhaps the background you would provide is already covered elsewhere in the book, for example. 

But it might also be that whatever you write as a first draft will need to be modified before it is accepted. You might have to do a lot of modifications so that the entire volume fits together properly.