Click on the Crop video button to use the tool. A picker will be shown to select the input video.
In the next screen, you can move the overlay window or four corner controls to select the desired crop window.
Click on Save video button to make output video. You can choose the output format (MP4 or WMV) and quality in the dialog. Then click on the Make movie button.
An other picker will be shown to select where to save the ouput video.
After the processing is complete, you can preview the output result.