If you are on a mac use imovie, or pc use windows movie maker...both come pre-installed and all you have to do is search your computer files for the program and then drag and drop onto your desktop
Windows Movie Maker will do a good job if you're after something basic and easy to learn, but if you need more power check out something like Sony Vegas.
This is a youtube video guide for basic video editing http://www.youtube.com/watch?v=tJxJVTma6Xs&list=UUAzTP_fJnFPlGtNVDmBbtjA&index=1&feature=plcp, though it is manily about how to make the video can be played on HTC One X. I think the way is easy, so you can have it a look.