Having an SSL (Secure Socket Layer) certificate does affect SEO. An SSL certificate is a sign that your website uses a secure connection to encrypt and protect user data. On a user’s browser, websites covered with an SSL certificate return a HTTPS URL (Hypertext Transfer Protocol Secure).
Such a website will allow users on modern browsers to access the site without any warning. A small padlock will appear in the upper left corner of your browser window. If you click on it, you can see that website’s SSL certificate, as well as your cookies and any collected site data.
If your website doesn’t have an SSL certificate, the user will get a warning your website is not secure. The padlock in the upper left corner will be replaced by a red exclamation point. Some modern browsers will not permit users from accessing HTTP (Hypertext Transfer Protocol – not Secure) URLs, at all.