InstantVNC is the application that allows remote access to your Windows PC. Simply distrubute this binary to the users you want to remotely support, and you'll be able to connect to them with an EchoVNC Viewer regardless of any intervening firewalls or routers.
As of the 2.0 release, InstantVNC can be used either in "as needed" mode, which requires no installation, or in an "always on" mode where it's installed as a normal Windows service.
When you first download it, InstantVNC is setup to connect to our demo echoServer at "demo.echovnc.com". To change that default, and to customize the binary for your community of users (e.g., changing the splash screen image shown at startup), simply hold down the SHIFT key while starting it up.