SSL is what puts the padlock and https in front of a website address.
Your own domain
When your domain reaches us, the screen shows Securing (SSL) and then Live. That means the certificate is in place. See Connect your own domain to your website.
The SSL menu
Catalog → SSL in your brand admin is for selling SSL certificates to customers. Selling them is switched off, so the page shows No certificates found. Nothing is wrong.
Common problems
My domain says Needs attention
Your domain reaches us, but SSL could not be added yet. We try again on our own a few times, or press Check now on Your domain.