?? Search Box. ??

Could someone please help us old guys out, and explain how the search box works! Does it search for all the words entered, inside the text, or only titles?
Also, under the search results, there is a gray box which says "Clear Selections", if I then "check" the boxes below that, does it clear (not search) those sections?
Is there a way to make it search for two words together, not separate words? Kind of confusing. Thanks for the help.
 
If you search from the home screen it searches the entire forum for the words you enter in the search box. If you search within one of the subtopics it searches just that subtopic. You have the option to check the boxes next to multiple areas to define where it searches. @Michael might have a better description of how search works. In general, I find that it works very well. It is important to remember that computers are fast but stupid. For example, it won't accommodate for spelling and typing errors, either in what you put in the search field, or in the text that it is searching. So if you type 'blue' but the article you're searching for has 'blew' you won't get a hit for that result.