First you need to log into STORM.

Once logged into STORM, you will be taken to the STORM dashboard.

You will need to have set up your website in STORM before you can install an SSL certificate on your site. Please see our Setting up a website guide with details on how to do this.

From the STORM dashboard click on Dashboard.

Click the cog icon next to your website to manage the settings for this specific site.

Click on SSL.

To Enable Let's Encrypt Click the Enable button

Now be patient, Let's Encrypt can take a minute or two to generate and apply the certificate. 

Additional Settings:

If you have multiple domains/alias you will be able to add an Let's Encrypt SSL for them as well, similar to doing it on the main domain but they will be listed at the bottom.

You can also do the HTTP to HTTPS redirect via STORM going to  Redirects 

And enabling HTTPS redirect