Add background image to TheMotion Homepage A top section

First, please install the   Advanced CSS Editor plugin and in Appearance -> Customize -> Advanced CSS Editor add the following code:

#featured-videos{
background-image: url('http://lorempixel.com/1366/720/');
}

Change the link above to the link where your image is located on your website. You could find the image link by going to WordPress Admin Dashboard->Media->Click on the image and copy the entire Url and substitute it in with the http://lorempixel.com/1366/720/. 

Save your changes and you're done.