Here’s a quick tutorial on Creating Slideshows in FCP from Contributing Member, Mike Greenberg of KonspiracyStudios.com:

I get this question a lot: What’s a fast and easy way to create slideshows in FCP?

1. Name your files in the order - alphabetical or numerical - that you want them to appear.
   • TIP: If you use numbers, add a couple zeros (e.g. 001.jpg) so that picture 20 doesn’t appear before picture 2.
   • TIP: If you have A LOT of pictures, try batch renaming them.
     
     
2. In FCP, hit Option+Q to pull up the User Preferences. Under the “Editing” tab, in the “”Still/Freeze Duration” field, set the amount of time that you what each pictures to appear.
3. Import your files into a bin.
4. Drag that bin to the timeline.
5. Now you have a slideshow. (Boring Huh?)
6. To add a dissolve transition between each photograph: (i) highlight the entire timeline and drag it into the Canvas; (ii) hold it until the placement options appear; and (iii) drop it in the Overwrite with Transition box.
   

   How bout them Apples? If you want a different type of transition, change you default transition.

Lightly edited by rich.