Click on the Trim video button to use the tool. A picker will be shown to select the input video.
In this screen, you can move the start or end control point to select the desired portion of the video.
Click on the Save video button to process the trimming. 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.