Windows Movie maker, free, but limited to some extent without research into how to do some stuff. As a beginner, it's a really good tool to use as you learn.
The Mac equivalent (iMovie) basics are easier to learn and advertised as more flexible- but the flexible add-ons are "built in" and not so easy to handle if you want to do things that are not "canned" options outside of the norm.
The more advanced softwares cost money but you can do stuff like add special effects (explosions, morphs, etc... lol).
Recommendation:
If you're a Mac user, start with free iMovie. Take the online tutorial lessons.
If a Windows user, start with MovieMaker.
They're both free, will accomplish the basics, and get you ready to do more if you want to go further. The "help" utilities and online help sites are really good.
JMO folks... respect offered.
Cheers,
OHM