Depending on where you live a router shouldn't be necessary for an office environment. Most office today run on fiber optic cable and this is run directly to the site. The cable will use a special type of network router that is hooked to a hub. Each device on the network will be cabled into the hub. The cabling from the computer to the hub should be a standard RJ45 ethernet cable. The cable is a pass-through cable that converts the fiber optic single and passes this single to your device.
However, if you are a small office with only two or three computers you can use a stand D-Link modem/router for your office. You will need to plug the phone line to the modem/router and configure the router for your internet carrier. Now, you can either use a WiFi connection or a cable connection to access the internet in the office.