Here are instructions on how to burn an iPhoto slideshow to a DVD. Specifically, these instructions are for people who have the current versions of iPhoto (9.5.1) and iDVD (7.1.2) and want the slideshow to automatically start playing when the disc is inserted into a DVD player. 

Here are step-by-step instructions on how to burn an iPhoto 9.5.1 slideshow to a DVD disc using iDVD 7.1.2. These instructions will likely work on some older versions of iPhoto 9 and possibly iPhoto 8, but I haven’t tested any older versions. [Note: iDVD has been discontinued. Version 7 was the last version made by Apple. It was part of iLife ’11. I believe this version of iDVD still works with macOS Sierra (aka OS X 10.12), the current version of the Mac operating system.]

1. Create the Slideshow in iPhoto.
2. In iPhoto select the slideshow on the left-hand list.
3. Click on the File menu and select Export.
4. Click the Slideshow tab and select one of the Formats. I would recommend 720p or 1080p (1080p is higher quality).
5. Uncheck the box to automatically send the slideshow to iTunes.
6. Click the Export button.
7. Name the file and save it to a convenient folder, such as the Desktop.
8. The export process can take quite a while to run, so go make a cup of tea.
9. Open iDVD and then go to the File menu and select One Step DVD from Movie. (You don’t need to select anything from the initial screen that offers you options like creating a new project or opening an existing project.)
10. Select the exported movie that you created above. Insert a blank DVD and wait for it to be burned.

The resulting DVD should then work in any standard DVD player that people would have in their living room and/or in their computer. Specifically, this DVD will automatically start to display the slideshow when it’s inserted. If don’t want your slideshow to auto-play then you should alternatively select your slideshow from the left-hand list in iPhoto and click the Export button that appears at the bottom of the iPhoto window. This will send the slideshow to iDVD, but require you to select one of iDVD’s Themes which will add a menu of choices. This menu will appear when the DVD is inserted and the viewer must select the Play button from the menu.