Install a Let's Encrypt Certificate

Certbot requires Snap. Install snapd and enable classic Snap support.
$ sudo apt install snapd

Install the core Snap to get the latest snapd.
$ sudo snap install core 

Update core Snap.
$ sudo snap refresh core 

Verify there are no Certbot packages installed with apt.
$ sudo apt remove certbot 

Install Certbot with Snap.
$ sudo snap install --classic certbot 

Link Certbot to /usr/bin.
$ sudo ln -s /snap/bin/certbot /usr/bin/certbot 

Request a certificate for your server. 
Replace the example email and domains your values. 

$ sudo certbot --nginx --agree-tos --redirect --email [email protected] -d -d

Test your SSL configuration on an SSL check website like SSL Labs.