I was trying to add a fade in / fade out effect to show a png image with text over a video. So I added the image (dark yellow strip dry.png in below image), cut in in three parts to use: fade-in; default image; fade-out.
Then I change the image Compositing to “Alpha Over” and with it selected the first image (left dark yellow strip) I added the fade-in effect: Add -> Fade -> Fade in. And did the similar to the most right strip, but added fade-out.