To add photos to your listing go to Boats > Manage > Photos (pictured below).
You can then either drag pictures into the grey box or press "Click Here To Select Files". To reorder your photos, grab a photo and drag it where you'd like it to go. Your first photo is the most important since it’s the one that displays in search results. To change your first photo, grab the photo you'd like to be first, then drag it in front of the existing first photo (pictured below).