Adding a shop button to the 'Salava' theme is quite easy:
Code modifications:Open Themes/salava/Index.template.php (file path may differ)Find:
// The [calendar]!
if ($context['allow_calendar'])
echo '<a href="', $scripturl, '?action=calendar">Calendar</a>';
Add after:
echo '<a href="', $scripturl, '?action=shop">Shop</a>';
Then, your shop button should be working