If you want to edit videos on your Windows PC, you'll need a video editing app. There's a free one called Movie Maker bundled with Windows Live Essentials, which you can download from Microsoft.
If you want something a little more sophistcated, you might wish to take a look at Vivideo from Wondershare. It allows you to create and edit your videos, based on clips that you import from your camera or hard disk. You can change the transition effects between scenes or clips, add annotations, and loads more too.
Vivideo normally costs $40, but until Christmas Day you can get it for free. Just head to http://www.wondershare.com/topic/christmas/giveaway.html and follow the instructions. You need to start by playing a game, which basically involves watching 4 short (around a minute each) videos on Youtube and clicking on the answers to some simple questions. Once you've answered the final question, you'll be given a password.
Next, go back to the link mentioned above, enter your email address and the password. You can then download the program and request a licence code. You'll need to enter the licence code when you run the program for the first time, otherwise it stays in 30-day evaluation mode.
Vivideo is a 20 MB download and runs on all recent versions of Windows. I've scanned the installer with VirusTotal and it gets a clean bill of health.