There are mainly 3 steps to enable https on your webserver:1. Using openssl command generate .csr and .key files.openssl req -new -newkey rsa:2048 -nodes -keyout domainname_com.key -out domainname_com.csr2. Buy SSL certificate from a vendor. You will need .csr file at the time of purchase3. Update nginx configuration file of your domain.Look at the link for more details: https://comodosslstore.com/blog/installing-comodo-positivessl-certificate-on-nginx.html