Hi,
1. The specifications tab is only displayed when there is things to display in it, like product weight, dimensions, etc.
2. To add a tab or add content in a tab, you have to edit the view "product / show_tabular" via the menu Display > Views and add an entry like:
<li id="hikashop_show_tabular_custom_li" class="hikashop_tabs_li ui-corner-top"><a onclick="displayTab('hikashop_show_tabular_custom');" href="javascript:void(0);"><?php echo JText::_('YOUR_TAB_NAME');?></a></li>
In the
<ul class="hikashop_tabs_ul"> element.
Then add a div with content after the "ul" thanks to:
<div class="hikashop_tabs_content" id="hikashop_show_tabular_custom">
<!-- Your div content -->
</div>
It require some HTML knowledge.