So what is the difference between a keyword and a key phrase?
A keyword is a single word, and a key phrase is two or more words that go together as a natural unit.
Let's look at some examples:
"Lord of the Rings"
"World War II"
In each case, the phrase is something very specific. If you don't keep the words together using quotation marks you lose the meaning of the phrase when searching. Remember, Galileo can't guess what you're looking for. You have to be very specific with your search!
Doing research for a literature class? Even book titles should be treated as phrases! It makes your search that much more specific, and helps you get the best results. Along the same lines, it is also helpful to do the same for a person's name. If are looking for information about Tennessee Williams, and that's all you use in your search (without quotation marks), you could easily get articles about some other person named WIlliams who happens to live in Tennessee!