First check if certbot is installed in your machine:
which certbot
If not installed:
sudo add-apt-repository ppa:certbot/certbot
sudo apt-get update
sudo apt-get install python-certbot-apache
Generating the SSL certificate for Apache using Certbot is quite straightforward. The client will automatically obtain and install a new SSL certificate that is valid for the domains provided as parameters.
To execute the interactive installation and obtain a certificate that covers only a single domain, run the certbot command like so, where example.com is your domain:
sudo certbot --apache -d example.com
If you want to install a single certificate that is valid for multiple domains or subdomains, you can pass them as additional parameters to the command. The first domain name in the list of parameters will be the base domain used by Let’s Encrypt to create the certificate, and for that reason we recommend that you pass the bare top-level domain name as first in the list, followed by any additional subdomains or aliases:
sudo certbot --apache -d example.com -d www.example.com
For this example, the base domain will be example.com.
If you have multiple virtual hosts, you should run certbot once for each to generate a new certificate for each. You can distribute multiple domains and subdomains across your virtual hosts in any way.
After the dependencies are installed, you will be presented with a step-by-step guide to customize your certificate options. You will be asked to provide an email address for lost key recovery and notices, and you will be able to choose between enabling both http and httpsaccess or forcing all requests to redirect to https. It is usually safest to require https, unless you have a specific need for unencrypted http traffic.
When the installation is finished, you should be able to find the generated certificate files at /etc/letsencrypt/live. You can verify the status of your SSL certificate with the following link (don’t forget to replace example.com with your base domain)