What is the definition and calculation for change in kinetic energy?

[bearhug]

Can someone give me a clear definition for the change in kinetic energy and how it's determined? The definition in my book doesn't really explain it really well.
Thanks

 

[Astronuc]

What is the expression for kinetic energy of mass m moving at some speed (magnitude of velocity) v? If m is constant, what variable must change in order to change kinetic energy?