I learned something Friday in my son's 4th grade computer lab. Isn't it a strange feeling when we volunteer at the school to help teach the kids and end up learning something new ourselves? I remember hearing that using the + and - signs were somehow helpful when using an internet search engine, but my son's teacher really made it simple and understandable for me.
Most important, in my opinion, is using the "quotation marks" around a search phrase. Say for instance I were searching for South America. If I just type in south america into the search engine box, the results will show things about south america, and other results for the word south, and also for the word america. Putting the term in double quotes forces the search engine to search only for the phrase, "South America". Or let's say you want to look up a man named Dave Smith. Unless you put that in quotes, then the search engine will also give you info on a bunch of people named Dave and another bunch of people named Smith.
The + and - signs are also useful. When looking up several words, you can force the search engine to look up a word exactly as you typed it, and not to search for synonyms, by using the + sign. Just put the + in front of a word with no space in between.
And the minus sign allows you to exclude certain words from your search. Just type the - sign in front of a word with no space in between the minus sign and the word you wish to exclude.
Here are more tips from the Google support web page:
# Phrase search ("")
By putting double quotes around a set of words, you are telling Google to consider the exact words in that exact order without any change. Google already uses the order and the fact that the words are together as a very strong signal and will stray from it only for a good reason, so quotes are usually unnecessary. By insisting on phrase search you might be missing good results accidentally. For example, a search for [ "Alexander Bell" ] (with quotes) will miss the pages that refer to Alexander G. Bell.
# Search within a specific website (site:)
Google allows you to specify that your search results must come from a given website. For example, the query [ iraq site:nytimes.com ] will return pages about Iraq but only from nytimes.com. The simpler queries [ iraq nytimes.com ] or [ iraq New York Times ] will usually be just as good, though they might return results from other sites that mention the New York Times. You can also specify a whole class of sites, for example [ iraq site:.gov ] will return results only from a .gov domain and [ iraq site:.iq ] will return results only from Iraqi sites.
# Words you want to exclude (-)
Attaching a minus sign immediately before a word indicates that you do not want pages that contain this word to appear in your results. The minus sign should appear immediately before the word and should be preceded with a space. For example, in the query [ anti-virus software ], the minus sign is used as a hypen and will not be interpreted as an exclusion symbol; whereas the query [ anti-virus -software ] will search for the words 'anti-virus' but exclude references to software. You can exclude as many words as you want by using the - sign in front of all of them, for example [ jaguar -cars -football -os ].
# Fill in the blanks (*)
The *, or wildcard, is a little-known feature that can be very powerful. If you include * within a query, it tells Google to try to treat the star as a placeholder for any unknown term(s) and then find the best matches. For example, the search [ Google * ] will give you results about many of Google's products (go to next page and next page -- we have many products). The query [ Obama voted * on the * bill ] will give you stories about different votes on different bills. Note that the * operator works only on whole words, not parts of words.
# Search exactly as is (+)
Google employs synonyms automatically, so that it finds pages that mention, for example, childcare for the query [ child care ] (with a space), or California history for the query [ ca history ]. But sometimes Google helps out a little too much and gives you a synonym when you don't really want it. By attaching a + immediately before a word (remember, don't add a space after the +), you are telling Google to match that word precisely as you typed it. Putting double quotes around the word will do the same thing.