[this post will be properly edited]

sudo a2enmod ssl
sudo service apache2 restart
sudo mkdir /etc/apache2/ssl
sudo nano /etc/apache2/sites-available/default

ServerName example.com:443

SSLEngine on
SSLCertificateFile /etc/apache2/ssl/apache.crt
SSLCertificateKeyFile /etc/apache2/ssl/apache.key

sudo a2ensite default
sudo service apache2 reload

source: digitalocean