Installing a web server under Debian is as simple as installing apache:
# wajig install apache
You will now have a default web page at http://localhost/. The actual page being displayed there comes from /var/www/index.html. You can begin creating your own web site from there.
For a secure web server, using SSL to encrypt all communications from a browser to the server (recognised with the https: prefix), there are at least two options in Debian. One is to use apache with the libapache-mod-ssl module and the other is to install the apache-ssl which installs a separate apache server to listen to port 443 (instead of 80). There are advantages either way but using apache-ssl is straightforward and cleanly keeps the two servers separate (configuration files are in /etc/apache and /etc/apache-ssl and log files in /var/log/apache and /var/log/apache-ssl respectively).