T&P Gallery Slider for WordPress is an image hover/click gallery as a WordPress plugin.
Make sure that there is a wp_footer() func in your footer.php
Simple attach the images you wish to appear in the gallery to the page or post where you will place the shortcode [tp_gallery]. or slider from another post/page by passing his ID to the short code [tp_gallery post_id="id"].
You can use CSS to change the look and feel of the layout.
You can use CSS to change image and thumbnail sizes.
the full width of image size. If you make the images square or landscape depends on you. Portrait images are no good idea because the gallery will become too high and you can not see the big image (overflow: hidden;).