How to Enable Varnish for website

Hello,

The Varnish module has been installed with Apache and Nginx reverse proxy. The Varnish service is running but when I test the website it shows x-Cache instead of Varnish. But I did not find x-Cache installed on server.

Given below is the output of "cur -I <server IP>"
HTTP/1.1 200 OK
Server: nginx/1.12.2
Date: Sun, 08 Apr 2018 12:46:28 GMT
Content-Type: text/html
Content-Length: 5069
Connection: keep-alive
Vary: Accept-Encoding
Last-Modified: Tue, 24 Jan 2017 21:00:51 GMT
ETag: "13cd-546dd693ee6c0"
Accept-Ranges: bytes
X-Cache: HIT from Backend

I thought X-Cache IS a varnish header. (https://docs.acquia.com/acquia-cloud/performance/varnish/headers) look at x-cache. Should show HIT or MISS if it is varnish.