Go to your SMF 2.0 files in your webhost and find the 'Sources' folder; Click that and find the file called "Subs.php".
Search for:
'home' => array(
After that array add:
'shop' => array(
'title' => "Shop",
'href' => $scripturl . '?action=shop',
'show' => true,
'sub_buttons' => array(
),
),