You can easily modify the gallery for your own purposes by adding and removing pictures from the /gallery subfolder and updating the unordered-list in this page accordingly.
You can have multiple galleries if you so choose, but each one must follow the format found in gallery.shtml: images inside of <li> tags (i.e. list items) inside of a <ul> (i.e. unordered list) tag with a class of "gallery" inside of a <div> tag with a class of "gallery-center".
The title attribute of the <img> tags provides the text which will be displayed underneath the image.