Mihamina
Make sure your /etc/sysconfig/network-scripts/wlan0 (or eth1, whatever your interface may be) has the boot at enable option
On CLI as root:
iwconfig mode Managed
iwconfig ssid myessid
dhclient wlan0 (or whatever your interface may be)
That would make it work but if you have a DE use NetworkManager since you don't need to be root to issue the commands && once you've logged in to an essid i. e home, work, coffe-shop whatever it will remember for the next time.
Edik