Can you please tell me how to code html link, so that user can click and
download the entire folder?
HTML is a markup language - it tells the browser how the
webpage is 'marked up'. It's not something you "code"
in the sense of a programming language.
If some HTML contains an anchor tag then most browsers
will, when a user 'clicks' on a link(presented due to
the presence of the anchor tag), send a request for the
anchor tag's href attribute URI to a webserver.
Once that's done, it's the job of the webserver to respond.
There are a variety of ways to, at that point, "download
the entire folder", but they all require configuration
and/or programming on the webserver.
For example, you might be using Apache and PHP, and have
the URI be
http://www.example.com/download_dir/ and have
an index.php script in /download_dir which puts all the
files except itself that exist in /download_dir into
a ZIP file and then sends that to the browser, which will,
depending on the user's preferences, either open the
ZIP file or save it to their harddisk.
Also, how to code html link, so that user can open this folder directory?
For example, you might be using Apache, and have
the URI be
http://www.example.com/download_dir/
and not have any index document in /download_dir
(e.g. no index.php, index.html, etc.), and have
Apache configured to present a directory listing.
http://httpd.apache.org/docs/mod/mod_autoindex.html