To print a photo, select it and choose FilePrint....

Shotwell can also print multiple images in one page; to do this, select multiple images, choose FilePrint..., and in the Print dialog, choose the Image Settings tab. In Image Settings, choose one of the multiple-image-per-page options under Autosize.

If you would like to set formatting, paper size, and orientation options, choose the Page Setup tab in the Print dialog prior to printing.