Using the CENSOR effect you will see a box (or selectable oval) on the preview screen. Choose Black, Pixelate or Blur.
Position the box over the subject with the mouse and click the small green + sign to create the first keyframe.
Move the red cursor in the effect window until the subject moves out of the box. Reposition the box and another keyframe will be automatically created.
Repeat until satisfied. The keyframes, shown by blue dots in the effect window, can be dragged, deleted (right-click on one) and otherwise positioned.
If you make a mistake press <ctrl-Z> to backtrack, step-by-step. In this example the man's face was tracked and blurred...
Preview the effect with either preview or sequence play, or simply drag the red line in the effects window.
Record_2020_09_03_16_15_49_453.mp4