Step 1: Click the plus sign in the middle of the photo slot.
Step 2: You will be taken to your Gallery, but you can choose to upload photos from your desktop. You can also choose to select your photos from either your Gallery, Albums, or Tags.
Step 3: Once you have the photos that you want, simply click on the photo to select it for your project.
Step 4: Move to the next photo slot you want to fill and repeat from step 1!