When doing a Google search, there are several ways you can narrow your search.
The first, is to put your search term in quotes. For instance, let's do a search on hot air balloons. When I did the search without the quotation marks, I got 4,680,000 results. With the quotation marks, 1,040,000 results. I've already narrowed my search down significantly.
Now suppose you want to search only educational sites because you're looking for more scholarly information. Put your search in like this "hot air balloons" site:edu. Doing the search this way ended up with 5,000 results (remember, though, edu also will bring up elementary school websites, which may not be what you're looking for). You can search government sites by using site:gov (5,180 results), or organizational sites, like museums, clubs, and organizations, by using site:org (49,500 results). Of course, if you're simply looking to buy a hot air balloon, you can narrow your search to only commercial sites by adding site:com to your search term (621,000 results).