You need to have some basic knowledge of GIMP.
First
(This part of the tut was not covered in the video, i started recording i a little late.)
Open your image
then you want to duplicate that layer so there is 3 of them.
Now add a new white layer and make it so theres 3 of them, then move them so there alternating
Once you've done that your ready for the Video.
Enjoy!
How to Make Rain
Sorry you have to download it, i couldnt figure out how to just post it, o well