In Aperture, select the images you want to use in your Final Cut Pro Sequence.
This launches the Aperture to Final Cut Pro plugin and arranges your photos in order.

For each photo, you can set its duration in the sequence and select a transition to be used between that photo and the next. Select the photo in the sidebar, then choose a transition from the list.

Next, give your sequence a name and choose one of the Final Cut Pro video formats from the popup menu.

Finally, choose the Aperture Export Preset to use for creating your photos and click Export. You'll be asked to choose a location to save the generated files in. Aperture to Final Cut Pro will place the exported photos in this location and generate a file called "Sequence.xml". Sequence.xml is the file which describes the Final Cut Pro sequence containing your photos.

Finally, Aperture to Final Cut Pro will launch Final Cut Pro and automatically import Sequence.xml.