What is the meaning of the sentence in the course?

Question

<!--or--> what is the meaning of it?

Answer 1

<!--
Is the begining of a HTML comment and
-->
is to define the end of your comment.
Comments are there to describe your code for yourself and for workmates... or peoples like us reading code from others :P
So you can use it that way:

<!--Hi I'm a comment-->
<h1>The previous line is a comment and will only appear in the source code</h1>

Answer 2

It is comment. It doesn't display in web page.

Answer 3

Got it. Tanks for your help