How to Set Background Video With CSS or HTML, YT Background player also not working with my Theme?

I went to the link ( you gave me but i do not understand some of it's instructions such as:

simply paste the code below near the opening <body> tag of your web template.

Where is this found?

this is the file path to a list of what i have editable in my webmatrix : /public_html/irealtygroupcareers/wp-content/themes/vantage

also would clicking on the video lead the visitors to you tube? how to disable this as well if we set this video as our back ground?

The YT player doesn't seem to be working? its on our training page ( )but its not playing anything..

thank you