Uhm, good point, but inaccurate in several areas.
If you search for big black dog, it will search for websites with all those words in the site, then it will return sites with any of those words after the sites with all the words. If you search for "big black dog", it will search for sites with that exact phrase (not black big dog, but only big black dog). If you want to find sites with any one of big, black, or dog, then search for big OR black OR dog. If you want to exclude a word, you want to find black dogs, but not big ones, search for -big black dog.
I have a book all about Google (Google Hacks), if you're wondering where I get this info.
And, PacificRipper, if you're looking for an exact phrase, like a band called The Morbid Cheese Monster, search for "the morbid cheese monster", in quotes, and you'll find that exact phrase, rather than any site with those words in it. It will also include words that it normally omits, like how, about, the, a, etc.