In HTML, a comment begins with "<!--", ends with "-->" and does not contain "--" or ">" anywhere in the text of the comment (because some browsers may see "--" or ">" as the end of the comment). Putting HTML markup inside comments is chancey, and should be avoided.
<p>End of Section 1.</p> <!-- Next section needs illustrations --> <h2>Section 2: Data Input</h2> <!-- Show input screens here. Use screen captures, full-sized, cropped. --> <p>A standard set of input screens guides you through....
Note that comments are not allowed within tags, i.e. inline between "<" and ">".
Generally, using comments to "comment out" code is not a good idea. It easily strikes back. It's better code to actually remove the code, saving the old version as backup when needed.