Click on the Slow motion button to use the tool. A picker will be shown to select the input video.
In this screen, you can change the speed of video playing faster or slower.
Click on the Save video button to start the process. 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.