Honestly, it's best to use the resources provided by your school. The questions on your test are going to come from your text book, study guide, lectures, and any hand outs provided by your instructor.
It's great that you want to be prepared and study additional resources, but reading lots of different sites and information is likely to just confuse you and overwhelm you. Stick to reading your assigned text book, reviewing your lecture notes and power points.
It can be helpful to review charts and other information that breaks down the information into more simple terms, but try to stick to charts, rather than text book type explanations. Again, the best resources for your test will be the ones provided by your instructor.
Here's a few other AN threads with some links to charts that might help clarify the difference between IV fluids for you. http://allnurses.com/general-nursing-student/iv-fluids-chart-450275.html