to start with, you should identify firstly, the purpose of deploying the concentrator. is the objective to provide lan-lan vpn between branch office or remote vpn access for road warrior? you then need to decide whether authentication is against the local database or another authentication server, such as radius.
have a look at the url, you can find many many useful configuration examples.
http://www.cisco.com/en/US/products/hw/vpndevc/ps2284/prod_configuration_examples_list.html
