To fade in/out at the beginning/end of the video, please follow below steps:
1. Press "Import " button to load the video file to the Media Library.
2. Drag and drop the video file into the video track.
3. Find the Sample colors under Media tab, choose black and drag it at the beginning/end of the video.
4. To change the duration, you just need to put the mouse on the edge of the sample color and when it turns into , please drag it to the length you need. Or you could double click the sample color on timeline and adjust the duration directly.