To create an SSL certificate, you need to create a certificate request, the so-called CSR (Certificate Signing Request). To do this, you can use generator CSR.
On the generator page, fill in all the fields marked with an asterisk and click “Generate CSR". After creating a certificate request, a private key will also be generated. With this information, you can purchase a certificate from a certification authority or its reseller.
If a self-signed certificate is enough for you, you can install it by instructions.