Example

$database = JFactory::getDBO();
$query = "SELECT id"
       . "\n FROM #__menu"
       . "\n WHERE menutype='mainmenu'"
       . "\n AND published='1'"
       . "\n ORDER BY parent, ordering";
 
$database->setQuery( $query );
echo $database->explain ();

Result (spaces added for legibility)

<div style="background-color:#FFFFCC" align="left">
    <table cellspacing="1" cellpadding="2" border="0" bgcolor="#000000" align="center">
<pre>EXPLAIN SELECT id
 FROM jos_menu
 WHERE menutype='mainmenu'
 AND published='1'
 ORDER BY parent, ordering</pre>
    <tr>
        <th bgcolor="#ffffff">id</th>
        <th bgcolor="#ffffff">select_type</th>
        <th bgcolor="#ffffff">table</th>
        <th bgcolor="#ffffff">type</th>
        <th bgcolor="#ffffff">possible_keys</th>
        <th bgcolor="#ffffff">key</th>
        <th bgcolor="#ffffff">key_len</th>
        <th bgcolor="#ffffff">ref</th>
        <th bgcolor="#ffffff">rows</th>
        <th bgcolor="#ffffff">Extra</th>
    </tr>
    <tr>
        <td bgcolor="#ffffff">1</td>
        <td bgcolor="#ffffff">SIMPLE</td>
        <td bgcolor="#ffffff">jos_menu</td>
        <td bgcolor="#ffffff">ref</td>
        <td bgcolor="#ffffff">menutype</td>
        <td bgcolor="#ffffff">menutype</td>
        <td bgcolor="#ffffff">228</td>
        <td bgcolor="#ffffff">const</td>
        <td bgcolor="#ffffff">9</td>
        <td bgcolor="#ffffff">Using where; Using filesort</td>
    </tr>
</table>
<br />&nbsp;
</div>