An overlay is a great asset to add atmosphere or effects directly over your video footage. Hence the name overlay and by having a little knowledge about blend modes you can quickly get the desired look.
It’s the same as bringing in your footage and once in the media pool it is simply drag and drop.
You can trim overlays to the desired length and experiment with blend modes to change the look. Some overlays are png sequence files so ensure you do not have “view individual frames” selected on the media page.