How do you print photos from Mac OS Photos app?

Much like printing from other Mac applications, with one extra layout step:

Select one or more photos.

From the File menu, select the Print... entry.

Select Photos-specific print layout options, click Print.

Select general print options, click Print.

And if you do not have a photo printer and want to to have the photos printed by a professional print service, you have to install a project extension for this print service from the App Store. Apple does no longer provide any native apple print service.

• In Photos, select the photos,
• then go to the menu "File > Create > Prints > App Store"
• Select the app for a printing service and install it. Restart your Mac, and the printing service will now show in the "File > Create > Prints" menu.

See: Order professional prints of your photos in Photos on Mac – Apple Support (UK)