Where a layout appears
Display Settings: all products, selected products, position on the page, and loading assets only where they are needed.
The Display Settings panel decides where a layout shows up. It is the panel that most often explains why a gallery is not on the shop.
On every product
Display on All Products puts the layout on every product page. When this is ticked, the specific products field below it is ignored.
On products you choose
Or select specific products searches your catalogue and attaches the layout to the products you pick. Use this for a gallery that belongs to one range rather than the whole shop.
Position on the product page
Position on product page chooses which WooCommerce hook the layout attaches to. The options run from Before Product (Top of Page), through Before and After Add to Cart, to After Product (Bottom of Page), so the gallery can sit exactly where it belongs in your theme.
The Layouts tab shows the chosen hook in its Displayed column, as woocommerce_before_single_product_summary or woocommerce_after_add_to_cart_button, which is the quick way to see what a layout is doing without opening it.
Shortcode only
Display via Shortcode Only stops the layout appearing anywhere automatically. Use it when you intend to place the gallery by hand. Shortcode placement is Pro.
Load assets on specific pages
Select the pages where the plugin's CSS and JavaScript should load, so a shortcode on those pages can render. Leave it empty for pages that use no shortcode and nothing extra is loaded there.
This is the setting behind the performance answer: scripts and styles load only on pages that actually show a layout, and nothing runs at checkout.