See here how to add a collection to your website.

To add a collection to your site, you'll need to create an image gallery first:

• Go to Content → Media → Create a Collection.
• Choose a name for your collection and select the images.

Now, as you have created your collection, you can add it to a page:

• Navigate to Content, and choose Edit on the page where you'd like to add the collection.
• Now go to the bottom of the page and choose Add Collection.

To learn more about different display options or how to edit an already existing collection, go to Collections.