If you would prefer to order prints from a third-party service (or if Apple does not support your country), you will more than likely have to do it manually. There are a couple of things to be aware of when prepping your images for export that can save you time and money.
Export your images at the maximum quality possible. Many services will have limitations on the size and the file format of images that they will accept (although these limitations are not as severe as they once were). Most will accept JPEG and so you should set up an export preset to export a JPEG at 100 percent quality. Some labs will accept TIFF, so if you want, you can use the TIFF format. This may preserve better color, depending on the printing process, but in all likelihood, a full quality JPEG is probably good enough.
Check with your printing service what color space or color profile they want their image in. If you are using a consumer lab, you should use the sRGB profile...