You are using Windows 8, the best, easy to use and free tool in Windows is the Windows Live Movie maker. This down to earth tool is one of my favorite tool to edit and upload videos to Youtube. You can easily cut and combine videos, can add background scores, narration and photos from your collection. It can upload directly to Youtube or can save it your local hard disk as HD video.
If you are so serious about video editing for documentary and movie creation, then you need some advanced tools like Adobe Premiere Pro, Sony Vegas, Cyberlink power director, Corel video studio and Sony Vegas movie studio, etc. But it cost more.
If you are looking for a free alternative you can download and use Lightworks it is designed by editors, for editors. An open source free 3D content creation suite Blender is also available.
Some other free tools are ZS4 Video Editor , Avidemux , </a> (a light weight tool), Movica, AVIedit, etc. You can find these stuffs using search engine. The premium stuffs are CyberLink PowerDirector,Corel VideoStudio Pro,Adobe Premiere Elements,MAGIX Movie Edit Pro, Sony Movie Studio Platinum Suite,Roxio Creator,VideoPad,AVS Video Editor,Pinnacle Studio,Sony Movie Studio Platinum,etc.
The list is too big and the tools are from basic to advanced. The most popular tool among movie/documentry editors are Adobe Premier Pro and Sony Vegas. Remember, the advanced tools are very resource hungry, princely and need in depth study to get a good result. For a layman, Windows Live Movie maker and Avidemux is enough. Keep in mind that the knowledge in the tool you are using and the editing skills decides your success. Knowledge is gained by learning and skill by practice. So stick to one tool that best suites your needs and try to master in it. Best of Luck !