====== Networking - defaults ======
You can configure networking per interface by editing /etc/hostname.XXX file where XXX is your interface name (em0/iwn0/...)\\
Example /etc/hostname.iwn0:
<code>
nwid YourNiceSSID
wpakey WPAkeyYouHave
dhcp
</code>
This will allow you to connect to the network YourNiceSSID simply by
<code>
sh /etc/netstart iwn0
</code>

====== Networkng - Manual ======
Example:
<code>
 ifconfig iwn0 nwid "YourNiceSSID" wpakey "WPAkeyYouHave"
</code>
Is equivalent to the above /etc/hostname.iwn0 example