When all the required photos are in the correct order, a menu entry is required so they can be viewed from the front end. Add a new menu entry in the usual way, and select "Menu Item Type" as Event Gallery > Event image list. Then select the Event you have just created and finish off editing and saving the menu entry. The gallery will then appear on the front end of your website, with one main picture, then a series of thumbnails.

If you prefer a different layout, then instead of selecting "Image list", you could select a different option. The decision about which layout to choose is a personal one, but to some extent it depends on the number of photos in the gallery.