Hello,
I actually found the freebsd handbook to be a bit useless in this respect in the way that it always gave examples using inetd and putting parameters into your rc.conf file.
For a wireless device, I find this is daft.
Have a look at the wpa_supplicant.conf example file for how to craft the wpa_supplicant file. Once that is done, it is usually as simple as...
# wpa_supplicant -Dbsd -iath0 -c/etc/wpa_supplicant.conf
# dhclient ath0
*This is done from memory so some spelling mistakes may occur
I use wpa_supplicant for anything wireless related now rather than using ifconfig and all that.
Hope this helps.