Answers for "how to set a link to a file that is not in the same folder html"

how to set a link to a file that is not in the same folder html

Within the same folder, just use the file name:

<a href="theFile.html">my link</a>

Within the parent folder's directory:
<a href="../theFile.html">my link</a>

Within a sub-directory:
<a href="theSubDirectory/thefile.html">my link</a>