For video editing, our favorite tool is Final Cut. But it is expensive. Check to see if it is available on library or computer lab workstations.
iMovie is much less expensive, simpler, and easier to use than Final Cut. However, it is more limited. One frustrating aspect is that it doesn’t let you use a still that is less than a tenth (or a fourth, in some versions) of a second. This can be prohibitively slow for animation.
There are many tutorials online for using these tools, so we won’t go into detail about them here. Just google around. And let us know if you find free software that works well for your animation, so we can share the tip.