If you are using an unusual codec (or using older hardware that uses interlacing) you would need one of the good free programs, such as HandBrake to prepare your clips for whatever editor you end up preferring. It takes all of the usual codecs I throw at it, as I often mix clips from different cameras, even GoPros. I actually learned about a feature that I didn't know existed. Plus, it's free or close to it - there are a couple of good books on it and, coincidentally, I just took one of the free classes at an Apple Store. It has a wealth of audio, exposure correcting, cropping, PIP, stabilization, transition, and title tools. I have a copy of FCP but haven't used it as I don't see where it does a better job than iMovie for 99% of people.
However, iMovie, mentioned by an earlier poster is quite advanced (latest version) and I've been using it for years to make instruction videos, videos that need voice over added, sports videos, as well as student performances and presentations.