How to record an App Preview

1. Connect your iPhone or iPad to you Mac
2. Open Quick Time Player
3. From the File menu, Choose new Movie recording
4. Fromt the drop down next to the record button choose you iphone/ipad for video and microphone
5. Click record
6. Do steps
7. Click Stop
8. File | Save
9. Add name, click Save
10. Close quick time player
11. Open imovie
12. From the File menu, choose new app preview
you may have to go back to the projects screen first
13. If you get the app previews info screen click OK
14. Drag and drop your recording from steps 1-9 into the bottom half of the iMovies window
15. File | Share | App Preview 
Or use the share button in the top right corner and choose app preview
16. Type a new title if required and click next
17. Type name if required, click save
18. Wait for iMovie to process
19. Click Close
20. Exit iMovie