It is one of the expectations of essay-writing at university level that all sources should be referenced, which means giving enough details about the book or journal article you have used for your reader to be able to find the passage you have used. This means giving a page number, or page range, as well as all the other details, since you can't expect your reader to search through an entire book just to find your citation. In most referencing systems, these details are included in a footnote or endnote.
You need to reference any source containing a passage you discuss, paraphrase or summarize, not just sources from which you include a direct quotation. It can often be a good idea just briefly to summarize something in the secondary literature to which you want to refer, and include a page reference for the passage, rather than quote directly, as this both saves space and shows that you have understood the key issues.
You will be able to find detailed information about different referencing systems in the library. For books, the key information is the author, the title, the publisher, the place of publication and the year published (as well as the page number of the passage); for journal articles, you need to give the author, the article title, the journal title, the volume of the journal, the year of publication and the article's page range (as well as the page number of the passage).
There is no quality control, in the form of peer review, for most of what is published on the web, so you need to think very carefully before using a website as a source. For web-published material, you need to give a minimum of the URL, and the date you accessed the page (the date is needed, because web-based material can change very quickly); the name of the author, and the date the page was created are also useful, if this information is available. The URL is the full address that appears in the address box of the web browser, including the specific name of the page - just giving an address such as www.victorianweb.org is not going to help your reader find the passage you're referring to, as there are probably hundreds of pages on the website.