Seimans 6520 adsl modem/4 port router

I use cable for my internet,,, Can i use this router/modem as a router for my home network? i can get the modem to see 2 comps ,,,, and the modem , by the lights sees the internet,,, but in the configuration does not see the internet.I have never set up a router before so im having problems.The router has an adsl port, usb port,4 ethernet ports , 1 of which can supposedly be used for lan wan. I have been able to get 1 comp connected to the internet with this router but ,no others. Could you please help. thanks for your input.