mid ocean ridges, sea floor spreading, plate tectonics

The following videos might help you understand mid ocean ridges and sea floor spreading:
http://www.youtube.com/watch?v=FQsbT9j3P44
http://www.youtube.com/watch?v=GyMLlLxbfa4&feature=related
http://www.youtube.com/watch?v=ifke1GsjNN0&feature=related

plate tectonics:
http://www.youtube.com/watch?v=nfziy_860GU&feature=related