In KSP, you must build a space-worthy craft, capable of flying its crew out into space, without killing them. At your disposal is a collection of parts, which must be assembled to create a functional ship. Each part has its own function and will affect the way a ship flies (or doesn't). So strap yourself in, and get ready to try some Rocket Science!
Some screenshots from the official site:
https://kerbalspaceprogram.com/index.php
A video showing rocket design and space flight in action: http://www.youtube.com/watch?v=l5OhFnq_iKw
