I will assuming you have an unframed X21 circuit, if you are using a WIC card. Therefore:
** Router A
interface Serial0/0
description WAN Connection to router B
ip address 10.1.1.1 255.255.255.252
** Router B
interface Serial0/0
description WAN Connection to router A
ip address 10.1.1.2 255.255.255.252
These routers would be communicating using a WAN protocol called HDLC. It is the default option. Default configuration commands tend to be hidden (though it is possible to unhide the commands). The above would enable each end to communicate between each other. However, any other connected networks, i.e. your LAN, would not be reachable by the opposite (neighbour) router.
Let me know how you get on.