Google automatically ignores many common words, such as "and," "or," "of," "a," etc. It also ignores some single digits or letters. This is usually not a bad thing, because the common words would just slow searches down without improving your results.
Occasionally it might be important to include one of these words in your search results. There are two ways to do this.
One technique is to use quotation marks. Anything inside quotation marks is automatically included in the search, and the search will include the exact phrase. For instance, "Rocky I" searches for the exact phrase Rocky I and will not find lyrics to "I Love Rocky Road."
Another way to force common words in your searches is with the plus sign. Searching for Rocky +I would find references to the movie and the Weird Al song. Make sure that you do put a space before the plus sign and do not put a space between the plus sign and the search word you want to include. Otherwise, the forced inclusion won't work.
In some search engines, you'd exclude words by using the "NOT" syntax. This doesn't work with Google. Use the minus sign instead.
If you were researching health issues, and you wanted to find out about pot bellies, you wouldn't want to find out about pot-bellied pigs. To conduct this search, you could type "pot bellied" -pig. Just as with the plus sign, put a space before the minus sign but do not put a space between the minus sign and the word or phrase you want excluded.
You can also exclude a phrase by enclosing it in quotation marks, so if you were researching livestock swine, you could search for pigs -"pot bellied" to exclude any mention of pot-bellied pigs. This wouldn't exclude pages that talked about pig bellies, because it only excludes the exact phrase "pot bellied."