Now that you have a router, you need to get it connected and online. If your service provider gave you a modem when they activated your Internet service, this should be pretty simple. Just follow these steps:
Turn off your modem,
Unplug the modem's Ethernet cable from the PC,
Connect that cable to the WAN or Internet port on your new router,
Power on your modem (wait for a minute or two),
Next power on your router (wait for a minute or two),
Now use another Ethernet cable to connect the PC to your router's LAN port, and
Turn on your PC.
By default, most consumer routers are set up to use DHCP to automatically assign an IP address to your computer. So if everything worked right, you should now be online.
If you are using an ISP-supplied router instead of a modem, things are a bit more complicated. First, you reconfigure the ISP's router to operate in bridge mode before you connect it to your new router. Bridge mode means the old router doesn't do anything to the network traffic and just passes it along to your new router for processing. While you can do this on your own, some providers will do it for you remotely once you make the request.
Once the ISP supplied router is in bridge mode, just follow the above steps to get your new router online.