What is lucid dream and how can someone learn to do it?

Lucid dreaming is the ability to be consciously awake in your dreams. This allows you to make active decisions in your dreams and even shape the dream world. It is very useful for not just entertainment (e.g. who doesn't like to fly like a bird?) but also for self-help (e.g. practice facing your fears like public speaking) and discovery. To best way to get better at lucid dreaming is to keep a dream journal (writing down your dreams very morning). I also suggest you buy the original book "Lucid Dreaming" by Stephen LaBerge.