Start by enabling the Certbot repository:

sudo add-apt-repository ppa:certbot/certbot

Next, update the package list:

sudo apt update

Next, install the Certbot Apache package:

sudo apt install python-certbot-apache

Finally, obtain the SSL certificate:

sudo certbot --apache -d example.com

Should you need to get certificates for multiple domains, simply add as follows:

-d domain1.com -d domain2.com

Note that the installed Certbot package adds a renew script to /etc/cron.d which will automatically take care of certificate renewal. This script runs twice daily.

To renew certificates manually you can run either of the following:

certbot certonly --webroot -w /var/www/html -d yourdomain.com

or

certbot --apache -d yourdomain.com