Citation (or reference) management software is used to organize your readings (journal articles, books, primary resources, reports, etc) as you are doing research. Besides organizing your research it also allows you easily to create your bibliography for papers, thesis and dissertations. There are quite a few of these tools available - some are free, most have fees (one-time or monthly).
Examples of the fee-based citation tools:
Examples of free citation tools:
Most library databases, used to discover journal articles, allows you to import the citation and sometimes the full-text PDF into the citation management software. However, not all citation management software is supported by the various databases and it can be very difficult (and frustrating) to follow the work-around to import citations. Unfortunately most of the free software suffers from this problem.