You have to set the settings in a file in /etc/vpnc

#sudo gainroot
Put the first 4 lines to match the connection details... in the file below. You can swap test.conf
#vi /etc/vpnc/test.conf

IPSec gateway the.address.or.ip.of.server
IPSec ID group.name.given.to.you.by.administrator
IPSec secret group.password.given.to.you.by.administrator
Xauth username your.username.given.to.you.by.administrator


From a root-shell you can then run:
#vpnc test

To close the connection
#vpnc-disconnect