The video just starts up again with no need to refresh or click on anything. Of note, Google (the owner of YouTube) has implemented its own server-side loop technology, and the video will start playing again without even needing to reload the browser page.
Return to your video and, once it’s complete, the video will automatically start over at the beginning. Here’s how to to put YouTube videos on an infinite loop using YouTube itself rather than an external solution. How to Put a YouTube Video on Loop (Repeat) on a PC
