Citation or bibliographic managment programs help you:
Each program works somewhat differently, so take some time to get to know a few programs and find the one that works best for you.
Don't worry about changing a program that isn't working for you. You can export your references from one program to another easily.
Why use Mendeley?
Why use EndNote?
Why use Zotero?
If you choose to format your references yourself, you can use programs such as ZoteroBib, but for formatting by hand or to check the work of a program, use these helpful examples from University College of the University of Maryland.