It is important to keep track of any sources that you may wish to cite later. You should ensure you have a record of:
the bibliographic details of your sources, so that means all the information that you will need in order to cite it;
the page numbers of any text that you may wish to use as direct quotes in your work;
the full text of articles, or a link to access them.
Reference management software is recommended to help you save time, keep track of your references, store and annotate full text documents and for collaborating with a study group, your tutor or other researchers.