You can add a free Let's Encrypt certificate from the Settings > Domains > SSL certificates view. All you have to do is tick the domain or domains to which you'd like to add a certificate.
You can get an option to add your own certificate by another service provider by subscribing to our Premium plan.
Forcing SSL
For using only encrypted traffic on your website, you can choose to Force SSL. Go to your domains menu and click on the cogwheel icon behind the domain name, find Force SSL and choose the Always use SSL option.
NB! Make sure the SSL certificate is activated before you force SSL.
You can check that by typing your website's address on the URL bar with the https:// prefix and when it displays your site, you're good to go. Otherwise, you lose access to your website.