You google for "embedding a video in html" and other variants of that phrase until you find a tutorial detailing the <embed> tag or the <object> tag.
This is a PHP website. Embedding a video in your site isn't a PHP issue, it's basic HTML. If you need to learn how to pull video links from a database and update them automatically or something, and you've achieved at least some rudimentary code, then come back and talk to us.