you must have php knowledge to add custom template bits.
go to acp->tempaltes&styles->templates->*yourtemplate*->click "add template" on top
Template Name: enter a name
Template Set: select global or your template name (global preferred)
Add the php or html code in the box.
and save.
this is the sample index_boardstats code
<table border="0" cellspacing="{$theme['borderwidth']}" cellpadding="{$theme['tablespace']}" class="tborder">
<thead>
<tr>
<td class="thead">
<div class="expcolimage"><img src="{$theme['imgdir']}/collapse{$collapsedimg['boardstats']}.gif" id="boardstats_img" class="expander" alt="[-]" title="[-]" /></div>
<div><strong>{$lang->boardstats}</strong></div>
</td>
</tr>
</thead>
<tbody style="{$collapsed['boardstats_e']}" id="boardstats_e">
{$whosonline}
{$birthdays}
{$forumstats}
</tbody>
</table>
and this code controls the minimizing and maximizing the box
<div class="expcolimage"><img src="{$theme['imgdir']}/collapse{$collapsedimg['boardstats']}.gif" id="X_img" class="expander" alt="[-]" title="[-]" /></div>
<div><strong>X</strong></div>
</td>
</tr>
</thead>
<tbody style="{$collapsed['X_e']}" id="X_e">
^^ replace all X with the template name you created.
By this you have created the template. Now you must call this template somewhere. So you must evaluate the template.
Open forum/index.php file and add this evaluation code at the place you want it to call. If you want it in the header, look for the header evaluation codes and add this code below them. --->
eval("\$Y = \"".$templates->get("X")."\";");
^^ replace X with the template name you created and replace Y with the name you would like to call ex:custom1
finally, if you want to call this template in header go to acp->templates&styles->templates->*your template*->header templates->header
and add this code somewhere
{$Y}
Y is the name you had given above to call it.