You should cite all sources (both printed and online) correctly and fully so that those who read your work can find and refer to your citations. When you are gathering sources for your topic, make sure that you note the following information for your citations[1]

For paper resources:

There are many reference management software tools available including: Zotero, EndNote, RefWorks, ProCite, CiteUlike, Connotea, Mendeley among others.

When choosing bibliographic management software you may consider the following: the price, storage mode, source from which it can import  information, the output, the ease of use, the integration with text processing software.