A router allows using multiple computers on one internet service. Many routers have wireless capability and thereby allow wireless connectivity with laptop computers with built-in wireless receivers or with desktop computers using a wireless adapter.
Are using a laptop computer? Is so, a wireless router would a solution for you. Using a cabled connection to the router, instead of wireless, means a cable would need to be run from upper floor to basement, or vice versa, depending on where the modem is located. Wireless would avoid the need to run the cable between floor levels.
