1. Tap the camera icon in the bottom middle of the screen.
2. Tap the button to the left of the red shutter button.
3. Select "a video" or "photos" etc. depending on which you want to use.
4. Tap on the photos you'd like to use, then tap "Done"
5. Tap the green play icon in the lower right corner of the screen.
6. (Optionally) Adjust the speed using the slider that appears toward the bottom of the gif preview.
7. Tap the green check mark in the top right and you're good to go.