Present Continuous I am writing a book now.
He is writing a book now.
Present Simple I write books.
He writes books.
Present Perfect I have written a book.
He has written a book.
Present Perfect Continuous I have been writing a book.
He has been writing a book.
Past Simple I wrote a book yesterday.
He wrote a book yesterday.
Past Continuous I was writing a book all day long.
You were writing a book all day long.
Past Perfect I had written a book.
He had written a book.
Past Perfect Continuous I had been writing a book.
He had been writing a book.
Future Simple I will write a book.
He will write a book.
Future Continuous I will be writing a book.
He will be writing a book.
Future Perfect I will have written a book by the end of the week.
He will have written a book by the end of the week.
Future Perfect Continuous I will have been writing a book.
He will have been writing a book.