The search feature has always been a little confusing to get used to. There has always been a link to help right there to explain how it works, but I decided to move the info right up front. So now, if you click on Search at the top of any page, you'll see the help right below the box you type in.
If you've had trouble getting good results from the search function, hopefully this will help you out. It's actually quite powerful if you know how to use it.