Why are there 3 ways of saying my in french?

mon - masculine, ma - feminine, mes - plural (NB this is according to what is possessed and not who possesses the object)

eg: my table - ma table (because the Word table is feminine in French)

my book - mon livre (because the Word book (livre) is masculine in French)

my tables - mes tables (here the Word tables is plural because there are more than one of them)