The old saying: A picture is worth a 1000 words. In this 21st century, a video is worth a 1000 words.
Educreations Interactive Whiteboard (free)
Educreations turns your iPad into a recordable whiteboard. Creating a video tutorial is as simple as touching, tapping and talking.
ScreenChomp by TechSmith (free)
Record It. Sketch It. Share It. – to create a sharable, replay-able video that tells your story clearly. http://goo.gl/NZArV
Both apps are only for iPad and are easy to use. The apps both provide multiple ways to share the video: email, Facebook, Twitter. Click on the links to view a short example made with each of the apps. I used my finger to draw on the screen.