After installation, when starting PRTG Traffic Grapher for the first time, a window will appear showing the following information:

Clicking on the button in the middle of the page will launch the Add Sensor Wizard. Using this wizard, you can set up your first sensor(s) for monitoring.
PRTG Traffic Grapher is an easy to use Windows software for monitoring and classifying bandwidth usage. It provides system administrators with live readings and long-term usage trends for their network devices. The most common usage is bandwidth usage monitoring, but you can also monitor many other aspects of your network like memory and CPU utilizations.