Whenever you read anything (book, article, etc) it is worth noting down all the details, a summary of the key points, and direct quotes that may be of use. Noting these on a card is helpful. It is also useful to make a note of where you obtained the book or article, so that you can easily re-locate it if you need to refer back to the original text again.
There are bibliographic software packages available which can help you manage your references and insert citations into your documents. EndNote is available on University PCs for desktop use. There is also an online version called EndNote Basic (previously called EndNote Web or EndNote Online). More information about Endnote can be found in Libguides.