In all Editing Modes, you can flip, rotate, or scale video and images.
Select a clip then click on its "Edit" button.
The Editing Window will appear and you must click on the "Transform" tab.
To Rotate a clip, click on the rotate buttons "CCW" (Counterclockwise) or "CW" (Clockwise). This will rotate the clip -90 degrees or +90 degrees.
You can also flip the clip horizontally or vertically by clicking on the corresponding buttons.
When you scale an image/video you can reposition it to create a picture-in-picture.
If you are in timeline mode, remember to scale the image/video that is in a track above the main track so that it can be visible.
You can combine this technique with clip opacity to easily create custom watermarks.
For a visual tutorial on how to utilize the layering technique, please refer to 06:18 - 08:23 in this video: