Under Add To Site in your Toolbar, you will see Add A New Gallery Page. Here you can add any number of photo galleries to your website.
After clicking Add A New Gallery Page, you will be taken to the Page Options window where you can enter information about your gallery's page. More information can be found on Page Options. After entering the page information, click Save Changes to create the gallery page.
You will be taken to the new gallery page. The new gallery will appear as an editable box with the name you gave it. Click the Edit button in the top right corner of this box to add photos and a description.