The process is simple, you pick a music backing from the list of 20, then a visual style to go with the video and then you record your clips for each part. This is usually a sound like a drum bear or a note. Once you have given it your clips, you can then marvel as it works it's magic and creates a music video using the samples you gave it.
The app is a cool little thing, it's not really a game, but it's still quite fun to mess around with and create videos. You can upload directly to facebook and youtube to share easily. I've only had it for a few hours, and that's probably how long it will last me at most, but there are worse things you could do with £1.49. If you have an iphone, it's worth checking out and having a play around.
Here are some videos I did with Vid Rhythm: