Install certbot and letsencrypt

sudo apt install certbot letsencrypt

Create a certificate:

sudo certbot certonly --manual --preferred-challenges=dns

List Certificates:

sudo certbot certificates

References:

• https://medium.com/@saurabh6790/generate-wildcard-ssl-certificate-using-lets-encrypt-certbot-273e432794d7
  
• https://certbot.eff.org/docs/using.html#manual
  
• https://www.digitalocean.com/community/tutorials/how-to-secure-apache-with-let-s-encrypt-on-ubuntu-18-04
  
• https://www.tecmint.com/install-free-lets-encrypt-ssl-certificate-for-apache-on-debian-and-ubuntu/