//this is a sample code. Jeong Kyu Eum
//tool handler function
RadEditorCommandList["customhelp"] = 
//function name is not needed.
function(commandName,editor,oTool)
{        
       // RadEditor old version using editor.ShowDialog function
       // RadEditor Ajax version using editor.showExternalDialog function
       editor.showExternalDialog(
        "/common/plugins/RadEditorAjax/customhelp/customhelpAjax.aspx",null,470,500, 
        //function that is executed when the dialog is closed with the return value.
        //see Default.aspx file 
        function(sender, returnValue)
        {
        },
        null,
        'Help',
        true,
        Telerik.Web.UI.WindowBehaviors.Close + Telerik.Web.UI.WindowBehaviors.Move,
        false,
        true);
};