Anyone can write a book, but doing it well and marketing it are the issues you need to be concerned about. The more you can demonstrate your credentials and experience in the field you’re writing about, and the better you are at explaining things in written form, the easier it will be to sell.
Of course, spelling and grammar are very important too. Books, as well as online articles, won’t sell unless they offer value to the reader.
I would recommend starting by writing articles online. Once you have a portfolio of well-written content, you can either continue writing online to make money, or you can compile all of them into a book.
Residuals from online content are easier to achieve since you get paid from advertisers. People doing Google search don’t need to pay for the articles they find, but books don’t make money unless the reader is willing to pay for it.
My books don’t make as much money as my online articles. That has been my experience. However, if you’re in a position to travel and make presentations in libraries and bookstores for book-signings, you could make it feasible.