YOUR_IMAGE_URL is the url of your image. The current index.html file's location is the default's url.
ex: If your image is hosted in the same folder as index.html, YOUR_IMAGE_URL is just the name of your file with extension (eg: "background.png").
If your image is hosted in a folder under index.html's folder, YOUR_IMAGE_URL takes this form: "images/background.png".
This current line will display a background image and repeat it horizontaly and verticaly.
There's also a default color added.
More about this was covered in the tutorial.
° Display a logo.
Open the index.html file of your exported project in a notepad.
Somewhere in between the <body></body> tags, place :
<a href="YOUR_URL"><img src="YOUR_IMAGE_URL" /></a>
<a> makes the image clickable and sending the browser to YOUR_URL.
<img> is the image itself. YOUR_IMAGE_URL follows the same format as in the previous paragraph.
More about this was covered in the tutorial.