To add an image to the gallery page you need to click Gallery in the left hand column and then click "Add Gallery / Images". You then need to click on the Upload Images tab, browse for your image file, and then select the Newfield gallery. You can browse for as many images as you like, once you are ready click on the blue "Upload Images" button at the bottom.
Now click the Manage Gallery button and enter the Newfield gallery. All your images should be in there and in this page you can add any descriptions to your photos. Click "Save Changes" and your images should be up on the site.