add_action function in wordpress

[BSmelody]

well im learning to create a wordpress plugini downloaded one and read the codes, and i saw thisi assume 'foo' is the tag where it will add action to..but what does the array() exactly do?\[code\]add_action('foo', array('foo1', 'foo2'));\[/code\]i looked at http://codex.wordpress.org/Function_Reference/add_actionand there is no clear definition about it ..