So Varnish is really good caching thingy if you use drupal (or other stuff) so to see what it is doing and how, you can login to your server and try this commands.
varnishlog - See what Varnish is currently processing, you will get complete header info I think
varnishstat - Shows various information about varnish
varnishhist - Shows a histogram chart of the last 1,000 requests (by default) to the Varnish. Showing | as a hit on the cache and # as a miss. The more | to the left of the chart, the better.
service varnish restart - is command to use to restart and clear all Varnish cache
service varnish reload - will only reload settings (VCL file), cache is not flushed
and all the rest you can see here
http://blog.rac.me.uk/2009/11/29/linux-handy-varnish-commands/