These sites will help you understand plagiarism and how to avoid it:
Understanding and Preventing Plagiarism - from Accredited Schools Online
How to Avoid Plagiarism - video from Rutgers University
How to Recognize Plagiarism - tutorial from Indiana University
10 Types of Plagiarism - video from Turnitin.com
Avoiding Plagiarism - tips from Hamilton College, NY
The DBU Writing Center exists to help students write better papers. Their web site explains the services they provide, and includes great handouts (available online as PDFs) that will help you learn the ins and outs of APA, MLA, and Turabian styles.
Other sites that offer great information about citation styles:
Northern Michigan University - look under "User Guides"
Nova Southeastern University (Florida) - choose your style from the list
Purdue University OWL - (Online Writing Lab)
University of Wisconsin-Madison - choose your style from the list
Writing Rescue Guide for College Students - style guides, tips, and expert advice
Official Sites with links to the parent organizations, including purchase information for the official style handbooks:
Citation Machine can be used to make citations. Just choose the style, choose the type of source (book, anthology, article, etc.), then enter the information (author, title, etc.) requested. Submit the form and—presto!—you have a citation you can copy and paste into your document.
The programs listed below will help you collect, organize, and manage citations in any style you choose. Some programs will also help you format your paper in the appropriate style. (Commercial sites offer programs for purchase.)
Zotero - free!
Mendeley - free!
EazyPaper - commercial
EndNote - commercial
RefWorks - commercial