a2ensite - a script that enables the specified site (which contains a block) within the apache2 configuration by creating symlinks within /etc/apache2/sites-enabled
apache2 - popular web server. Alternative web servers are tomcat, nginx, etc.
openssl - SSL works by using a private key to encrypt data transferred over an SSL-enabled connection, thus thwarting eavesdropping of information. Use openssl to generate keys and certificates.
vim - a popular text editor