there are a few options available to make your two geographically dissimilar LANs communicate with each other.
first is a 'routed' approach. this is where you'll have a router at both sites, with an HDLC or pointToPoint link between them, say a T1.
you'll configure the LAN ports of the router(s) to connect to the local LAN of your site.
you'll then configure the WAN ports of the routers to connect them together via the WAN.
(the WAN requires a service provider such as verizon, att, etc. to provision a 'leased line' or other such link for your use between the sites)
NOTE: as far as WAN links go you have many options, T1, frameRelay, fractional-T1...etc.
or you can use a 'bridged' approach. the same WAN link will be required from a service provider but the routers will be configured slightly differently.
(instead of routing between the LAN-WAN-LAN, they'll be configured to bridge between the LAN-WAN-LAN)
you will use a 'bridged' configuration if you must due to an application or other requirement that cannot operate in a routed environment. (a routed configuration is more common but both are possible)
please see the following links for basic routing configuration of an HDLC link:
(for use with an integrated CSU in the WIC)
http://www.cisco.com/en/US/products/sw/iosswrel/ps1826/products_feature_guide09186a0080080f74.html
http://www.cisco.com/en/US/products/sw/iosswrel/ps5012/products_feature_guide09186a0080194a32.html#wp1032260
http://www.cisco.com/en/US/products/hw/modules/ps3129/products_tech_note09186a00800b1501.shtml#sample_cfg
please see the following link for a basic bridging configuration of an HDLC WAN link:
(for use with an integrated CSU in the WIC)
(same hardware and WAN link as above with bridged configuration)
http://www.cisco.com/en/US/products/hw/switches/ps5304/products_configuration_guide_chapter09186a00800f0a16.html
if you require more assistance, let us know more specifics about the WAN link & type, router model and LAN info and we can create a basic config for you.