Sharing bsnl broad band

Hello,
sir i wan to share my bsnl broad band with two pc's..if i use router will it be possible.i went through your answers for smilar question.but i din't get to what is ethernet card.so pls explain it clearly how to share the network..if we make one pc as server do we need to keep it on all the time, in order to use the clients..please exolain step by step.