Click on the Join videos button to use the tool. A picker will be shown to select the input videos.
In this screen, you can drag and drop video thumbnail to change its position. You can also add new video by click on the button Add video at the bottom bar.
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.