Calling onSaveEntry event only for one section
You would compare against the entry's section / entry type in a conditional. The entry modal is available from the event params $event-&gt;params['entry'].

craft()-&gt;on('entries.onSaveEntry', function(Event $event)
{
    $entry = $event-&gt;params['entry'];

    if($entry-&gt;section['handle'] == 'mySection' &amp;&amp; $entry-&gt;type['handle'] == 'myEntryType')
    {
        // Execute for mySection / myEntryType entries only!
    }
}