I think the app you're referring to is for iOS or Android devices only (via Apple or Google App Stores). I think the "quick start" guide they provide is not helpful in the slightest, and you don't need an app to set up a router. The full manual is here - http://www.downloads.netgear.com/files/GDC/R6080/R6080_UM_EN.pdf which I'd highly recommend downloading.
Essentially the steps will be
- Connect Ethernet cable from your modem to the Internet port on the router (as shown in manual page 12)
- Connect to the router with your computer (wireless setup can be done, but for intial setup it's recommended to use a wired connection). So plug an ethernet cable from your computer to one of the LAN ports on the router.
- Power everything up, wait for the modem to establish a connection (if it normally takes a minute or two to connect) and log in to the router using your web browser. The router is accessed by typing http://www.routerlogin.net into a browser address bar. This is a pre-programmed address that the router should recognise even before the internet connection has been established. This should run an automatic installation wizard as shown on page 16 of the manual. Follow the on screen instructions..
The wizard should take you through setting up the internet connection. How this is done will depend on your ISP, but I think most cable companies will use automatic IP address allocation, and don't require a username and password to connect. Refer to your ISP if necessary. More rarely, a static IP address may be assigned, which you would have to enter manually. Some connection methods require a username and password to connect, but as I understand it, that isn't usually the case with cable. As I use a DSL fibre connection, I have to connect using something called PPPoE (will likely be one of the connection options you see), which requires a username and password to connect (provided by the ISP).
It should also take you through setting up the wifi, changing the default passwords (never leave them at default) etc.