OpenShot is an open-source program for video editing that you can download for free.
OpenShot is also available on the library's check out laptops, though you'll want to save your files to a flash drive--the laptops delete all files whenever they're restarted!
iMovie (free on some Macs or can be downloaded for $14.99)
With a beautiful, streamlined design, iMovie puts the focus on your video and lets you tell stories like never before. Browse your video library, share favorite moments, and create beautiful HD movies and Hollywood-style trailers. And with iCloud, you can enjoy them in iMovie Theater on all your devices.