What is the correct way to write the word ebook? I need to know the rules for grammar.?

The word is a neologism, so the ruling may be up to the dictionary writers, the lexicographers. You might write to James Kilpatrick who has a syndicated column on the English language, its grammar and syntax. My own preference is for it to be NOT capitalized, but with a hypen. This is the clearest representation of the meaning of the word. It should NOT be capitalized, as it's not a proper noun. If it is part of a title or at the beginning, it would be capitalized. I don't like the word, so I might use something else. A book is a book is a book, no matter whether printed on paper with ink or stored in a more advanced medium.

I guess www.ebooks.com is the best source to find out this answer. They spell it eBook.... ....although it seems as if the format the file is in also affects the spelling. E-book Published as a ".doc" or ".txt" eBook Published as .pdf or .html Don't ask me why!