We will configure our routers and switches via console ports using a special console cable, which in our case has a RJ-45 connector at one end and a DB-9 connector at the other end. You are unlikely to find DB-9 ports on contemporary computers, thus we need to have a DB-9-USB adapter cable to be able to connect it to a USB port. You can see an example of such a cable and an adapter in the following images from the Cisco website:
You might need to install special drivers for using an adapter, so please check your adapter's user manual.
Alternatively, you can get a console cable with both RJ-45 and USB connectors, for example, on eBay (http://www.ebay.com/):