Open the folder you saved all your images in and simply drag and drop into the desired location. A little light green line will appear to let you know where you are about to drop your picture. You can drop all your images in and reorganize them later. Leave your folder open to make sure you added everything.
Alternatively if you already have photos in your iPhoto or Photo Booth you can open those in the "Photos" box in the bottom right corner using the "Photo" button.
To add a title or informational banner to the slide repeat the process in Step 6 and edit accordingly.