this is a great site (take a look).
Should you paraphrase or quote?
In general, use direct quotations only if you have a good reason. Most of your paper should be in your own words. Also, it's often conventional to quote more extensively from sources when you're writing a humanities paper, and to summarize from sources when you're writing in the social or natural sciences--but there are always exceptions.
In a literary analysis paper, for example, you''ll want to quote from the literary text rather than summarize, because part of your task in this kind of paper is to analyze the specific words and phrases an author uses.
In research papers, you should quote from a source
1. to show that an authority supports your point
2. to present a position or argument to critique or comment on
3. to include especially moving or historically significant language
4. to present a particularly well-stated passage whose meaning would be lost or changed if paraphrased or summarized.
You should summarize or paraphrase when
what you want from the source is the idea expressed, and not the specific language used to express it
you can express in fewer words what the key point of a source is.