How can I create the highlight oval on a family film to highlight someone on the video. They are moving.?

this isnt a simple process im afraid, and if you are asking here, chances are you won't be able to do it but here goes anyway. ideally, you want something like Adobe Premiere or Aftereffects. Probably the easiest way to do it would be to draw a white circle and make it semi transparent, then move along the timeline creating a motion tween to move the shape along over time.