I want to mix any part from video 1 and video 2 like above, part from video 1 will be in the left, part from video 2 will be in the right, so how to do that?
Put Video 1 on a track, and video 2 on another track right under it. Create a rectangular mask in video 1 using the pan/crop window, (checkbox at the bottom of the window). The part you mask will be hidden, and you can see the part of Video 2 that is below it. To move things around, uncheck MASK in the pan/crop windows, click on the Position keyframe bar just above the Mask bar, make your moves.