For an overview of what you can do in a standard editing program, check out this short, informative video from Vimeo's video school
Video 101: Editing Basics from Vimeo Video School on Vimeo.
Like this? More lessons can be found here.
Animoto can be used for free, as long as your video is not longer than 30 seconds. If this is too short for your project, then you may want to avail of some of the other freely available video editors listed on this page.
Masher is another free software that allows you to create a video mash-up in minutes. It has a built-in library of footage and music.
Windows Movie Maker
Windows Movie Maker is a free software download for PC users. It allows you to import movies, video, photos, and audio, choose a theme, and share on the web. Support for using this tool is available here.
iMovie is for Mac and iOS device users. If you're used to working in the Mac environment, you may prefer to use this tool. There is also an iMovie app for iOS which is free in the App Store.