A, An, The R ules for using articles often confuse students who learn English as their second language. A historian gave us a hand for an hour when we were planting an heirloom rose bush in a hothouse. Well, he confessed to stealing a car. That is the book you borrowed last month. In the first example, the second speaker implies that the other person may have borrowed more than one book last month.
Some general words take no article at all.
Words signifying things that cannot be counted easily. We're studying the history of knowledge. We like drinking the tea every afternoon at 4. Yesterday, John saw man he knew from his summer job. A apple a day keeps the doctor away.