1 New movie
Open up iMovie and, from the toolbar, select to create a new movie. This will present you with the various theme options. Take your time to choose the one that suits your project best.
2 iPhoto Library
With your new project named and open, click the iPhoto Library option. This will open your various iPhoto albums and events in the top-left preview window, ready to be browsed.
3 Drop in your photos
Having found the images you would like to include, use the Cmd key to click and select each of them. With them all highlighted they can be dropped onto your timeline.
Your photos will automatically be stitched together, complete with transitions. Double-click on any of these and you can edit the transition so that it suits the overall style of your slideshow.
Depending on the theme you chose, there will be an opening and closing screen that comes with text. Double-click on this in the timeline to edit it to match the theme of the slideshow.
6 Import a music track
Go to the Import tab at the top and you can go through your Mac and import music. This can come from iTunes and beyond; just select the track and click Import before dragging it in.