Whenever you refer to a specific passage of text without quotation you must also give the page reference. You would normally have several references per page, so that the reader knows the sources for all your information. Students sometimes fall into the trap of paraphrasing extended passages. Restating an argument in your own words does NOT mean copying chunks of text and changing only a few words here and there. Be sure to footnote all ideas you take from the books and articles you consult.
Plagiarism is an extremely serious offence.
Extended paraphrases and translations are also plagiarism. In accordance with university regulations, when I believe that an essay is plagiarised, I give the essay to the Associate Dean of the student's faculty. In my experience, the most common penalty for plagiarism is to be failed in the course.