I have at least one documentable plagiarism case every year. On occasion, there is malicious intent to deceve; more often, however, the plagarism occurs accidentally -- through laziness, carelessness, misunderstanding, or panic. No matter the intent, however, all forms of plagarism are equally in violation of the Academic Honesty Policy at this (and any) institution. (You can download the entire "A Culture of Honesty" policy book here.) As I state clearly in the syllabus,
You will be held responsible for the contents of any and all assignments you hand in. This means that, whether or not you intend to commit academic fraud, you will suffer the consequences if you do so. I expect all of my students to uphold the highest academic standards and ethical practices, and as a result have no sympathy with intellectual dishonesty cases that come across my desk.
How, then, do you keep from being one of those accidental plagarists?
I'm going to point you to a website hosted by Bates College in Maine. Take a look at it: start with "start here" link, then work through the Introduction and the tutorials. This site covers everything I might tell you, in more detail than I would likely present it here.
The three overarching pieces of advice I would give you would be not to procrastinate on assignments and to take clear and clean notes when consulting secondary (including internet) sources, then use those notes to acknowledge information properly.
As always, if you fear you are riding close to the edge of academic dishonesty, or if you're not sure what does and does not constitute "common knowledge" in any given field, please ask me or another professor. And when in doubt, it's better to overcite than undercite.
(In case you're wondering what all the plagarism fuss is about, I'd like to remind you that people outside the halls of Park Hall do indeed care, as evidenced by this November 2010 online copyright-infringement case that went viral: www.guardian.co.uk/media/pda/2010/nov/04/cooks-source-copyright-complaint.)