please explain what do you mean by donating book on the website?
Ok, in case you have some books, which you have finished reading and wanted to share or give away or just don't want to keep the books any more with you then you can simply create an Ad (so called donate book Ad) in donate-books.org website and let interested people (who ever wants those books from you) contact you and then you just pass on your books to him/her.
That's called donating your book.
Please note that you have to be a little bit patient after putting your donate books Ad and then let the interested people contact you and ask for your books.
Also, always use your best judgement while donating your books.