Router for 2 LANs

A client has 2 separate LANs with 2 sets of IP address per LAN. Do I need a router to access network resources to the 2nd LAN and vice versa? If so, do I need 2 routers-1 for LAN A and another 1 for LAN B?

Is there a way to access network resources without a need of a router? If so, how?

Where can I find diagram on how to configure and connect to LANs?