Mendeley is a free (up to a point) citation manager that you can use to manage your reference library and insert citations into documents.
Unlike some citation managers, Mendeley has a useful social networking feature that allows for you to follow and discover research. It also can recommend articles for you to read based off of what is in your library.
Image source: www.mendeley.com
Create an Account & Download Mendeley
To get started, go to the Mendeley homepage (www.mendeley.com) and click Create Account. This will prompt you to enter your account information for your Mendeley account.
After you create your Mendeley account, you will need to
Start up the desktop software for the first time and sign into your Mendeley account. You will be prompted to install the web importer (if you have not already) and to install the Microsoft Word plug-in (required if you want to use Mendeley to insert citations into documents).
You can always sign into your Mendeley library from Mendeley's homepage - you will be able to add, view, edit, and organize references, in addition to participating in groups and viewing suggested articles.