Under Content > Photo Galleries you will see the existing galleries. Above the preview of the galleries there is a link that says Create New Gallery.
The gallery editor takes you to General Edit. Add your desired title for the gallery and a short description. Under the Photos tab you can choose your file and add a title and caption. Once the desired amount of pictures are uploaded you can edit (blue pencil), delete (red X), and drag the images to sort.
As always, when you are editing or creating a gallery do not forget to save often. This will prevent any loss of work.
Under Content > Photo Galleries you will see the existing galleries. On the top of the preview there is a blue pencil. To edit the gallery click on the pencil.