After you install the module, go to Extensions -> Modules and find Web7 Video. After opening an administration of the module, you can see quick setup guide and important links.
Head over to Settings (third tab) and insert your Youtube video URL (It must be in a full format from the address window in your browser. Not the shortened one.)
After this step, choose the article you want to be shown over the video. You can select additional options such as showing headline, showing read more button etc.
At this point, you're pretty much good to go and publish the module in a position you choose. But we recommend you to set a height of the video in case you didn't create own CSS style.