user access passwords

I have a 2 routers connected through serial cable(routerA $ routerB). In routerA there exists a lan network connected to ethernet port(e0), there are 5 users in that. now i want to give different user passwords for different users in order to telnet to the routerA or routerB. how can i configure this. wwhich command i should use to configure it, plz help me out

thanks $ regards