Establishing the button in the toolbar

You should create a new toolbar in your custom Configuration File to reference the plugin:

//custom config.js - My custom Configuration File
FCKConfig.ToolbarSets['PluginTest'] = [
['SourceSimple'],
['My_Find','My_Replace','-','Placeholder'],
['StyleSimple','FontFormatSimple','FontNameSimple','FontSizeSimple'],
['Table','-','TableInsertRowAfter','TableDeleteRows','TableInsertColumnAfter','TableDeleteColumns','TableInsertCellAfter','TableDeleteCells','TableMergeCells','TableHorizontalSplitCell','TableCellProp'],
['Bold','Italic','-','OrderedList','UnorderedList','-','Link','Unlink'],
'/',
['My_BigStyle','-','Smiley','-','About']
] ;

In the given example, 'Placeholder', 'My_Find', 'My_replace' and the table commands are implemented by plugins.