If you want a still picture to move, please use the keyframe function. Key frames record the picture state at a certain point in time, such as the position of the picture, the enlargement and reduction of the picture and so on.
If you click two key frames at two times. Then the state of the video will change at this point in time.
For example, insert a picture-in-picture in the video, type a key frame at the beginning, drag the timeline, move the picture-in-picture at another time point, and then type a key frame, then the picture will move when playing.