Hi Michael,
I guess you know how to create a new module position in Joomla, right? Just define that new position in XML file of template. I called it 'newposition'.
Next, you go to the layout file of template that you're using on your site in this folder:
/templates/purity_iii/tpls/blocks/mainbody/
For example, your site: https://j4.sankt-barbara-muelheim.de/ is using layout with main content + 1 sidebar on the right, so you need to edit file:
/templates/purity_iii/tpls/blocks/mainbody/one-sidebar-right.php
(if other pages use other layout, you need to edit associated file)
Add this line of code above the message and component block:
<jdoc:include type="modules" name="<?php $this->_p('newposition') ?>" style="T3Xhtml"/>
It will look like this:
<div id="t3-mainbody" class="container t3-mainbody">
<div class="row">
<!-- MAIN CONTENT -->
<div id="t3-content" class="t3-content col-xs-12 col-sm-8 col-md-9">
<jdoc:include type="modules" name="<?php $this->_p('newposition') ?>" style="T3Xhtml"/>
<?php if($this->hasMessage()) : ?>
<jdoc:include type="message" />
<?php endif ?>
<jdoc:include type="component" />
</div>
<!-- //MAIN CONTENT -->
<!-- SIDEBAR RIGHT -->
<div class="t3-sidebar t3-sidebar-right col-xs-12 col-sm-4 col-md-3 <?php $this->_c($vars['sidebar']) ?>">
<jdoc:include type="modules" name="<?php $this->_p($vars['sidebar']) ?>" style="T3Xhtml" />
</div>
<!-- //SIDEBAR RIGHT -->
</div>
</div>
Then go to module in backend and assign module you wish to 'newposition' position + assign to correct menu item.
Regards