install / configure interface

I’m newbie in linux but i’ve some experience in netware and nt.. i found a problem in my linux server . there are two card in that server. eth0 was configured but eth1 was not. i’v try to use ifconfig to give ipaddr to eth1. that was success !!. but that was not permanent. if i restart my server, configuration for eth1 disppear..
maybe i must put the configuration in a file.
but i don’t know what file is that.
please , i need some explanation for the problem
thank’s