A Japanese particle is a word that determines the role (subject, object, etc.) of
          the word(s) preceding it.

          Because it follows the word it explains, some call it a "postposition."

In Japanese, the grammatical roles of some words in a sentence - subject,  direct object, and so on - are identified by particles, also known as postpositions.  These short words indicate the grammatical function of the word or phrase preceding them.  Particles are a key element of Japanese grammar.  (ようこそ1, 184)
 

      A Common Usage:

                 English                     Japanese
            ------------------------------------------------
                           I                                   わたし（は、が）
                          my                               わたしの
                          me                               わたし、わたしに、わたしを、etc.