Regardless of your installation method, once you have NGINX up and running, you should be able to browse to it via the IP address and/or Fully Qualified Domain Name (FQDN) and see something very similar to what is shown here:
Default NGINX page
To start, stop, and restart NGINX (if installed using official binaries), you can use the standard Linux init systems. There's a very slight variance between the different OS versions, so it's important to ensure you're using the correct command for the correct variant.
As Ubuntu switched to systemd as the default init system from 15.04, make sure you double check the version you're using.