A noun may be given a possessive suffix in a sentence to indicate
    posession of something else.  In most cases, possession is given the
    suffix -'s.
    
    Example: The spider's web.
    
    The above sentence tells the reader that the sentence refers to the
    web which belongs to the spider.  This sentence may also be read as
    "The web of the spider", which has the same meaning; it is easier to
    use the first example instead, however.
    
    There are also plural possessives, which are used when speaking of
    something belonging to more than one noun.  In most cases, plural
    possessives may be given the suffix -s'.
    
    Example:  The teachers' lounge.
    
    Writing "teacher's" instead of "teachers'" indicates that the lounge
    belongs to one teacher instead of more than one or all.
    
    When the normal spelling of a word ends with a final s, a lone
    apostrophe follows the word to indicate possession.
    
    Example: Haelis' Graveyard.
    
    Simply writing "Haelis Graveyard" will not do, since it would appear
    to the reader that Graveyard is Haelis' last name or the name of the
    graveyard is Haelis.  Haelis is a person, and the graveyard is his.


    NOTE:  If a noun is plural and not possessive, no apostrophes are
required.  

   Example:  My friends went to the movies.

  Incorrect:  My friend's went to the movie's.  

See also:  help grammar.