|Posting the exact make/model of the router would be helpful.|
Go to Linksys' website and search for the manual. Download it and read it through thoroughly before attempting to set it up.
Wireless "b" is old. Wireless "g" is the present standard and the wireless "n" is almost ratified into a standard (should be real soon). Each is progressively faster so you have "b" as the slowest and "n" as the fastest. Your equipment should probably be "b/g". Which means it's "g" but backwards compatible with "b" as well.