Your comes with a number of template pages for adding your dogs. Boy1, Boy2, Boy3, Girl1, Girl2, Girl3
You can open each of these pages and edit and change them to your dogs name and details, and add photos.
At the top you would change where it says Boy1 to your Boys name, then below that you can change the permalink (click the edit button first) to your boys name.
This will update the menu when you save the page.
If you need more pages than the template ones, to add your dogs, you can copy or clone one of the dogs pages to use the same template, and just change it as needed.
In the page attributes on the right of your edit pages you would select a parent page (Our Boys or Our Girls) then add a number in the order field so it will display in that order on the menu.