This page uses the "gallery" page type. The Edge theme includes all the styles necessary to use the excellent Sortable Fancybox Gallery add-on available for free from the Concrete5 website.
The ideal image size is 500 pixels wide by 434 pixels in height, although you could change the size if you keep the width to height ratio correct.
Thumbnails should be 212 pixels wide by 185 pixels in height.
This box is for information only, you don't need to have it on your gallery page.