Some researchers find it helpful to keep track of sources using a synthesis matrix. A synthesis matrix allows you describe and categorize what you've read. You can then sort the sources by categories and begin to synthesize the literature about a topic.
Citation management tools help organize and cite sources using technology. These tools also allow you to assign categories to what you have read. They typically have browser plug-ins to save the citations and information you find online. Most are able to be integrated into Word or Google Docs, allowing you to cite as you write.