You may refer to this website, it collects 10 free online video editing software, they work for both windows and mac, you don't have to download and install anything. They are not as professional as the software you need to install on your computer, but they are simple to learn and easy to use.
A very good program is sony vegas. There is a trial run for it and also if you want the full version you could pay or you could torrent it or even use a crack. Sony vegas is professional editing software I may add.
Download a desktop software to edit the video , use the AVS video editor which includes some powerful funtions. Or create your movie online