If you want to learn some basic stuff just do the basic missions.
if you want to be down with the hacker movement here are some good sites
a very good list of sites
hackthissite.org
phonelosers.org
textfiles.com
oldskoolphreak.com
phreaksandgeeks.com
docdroppers.org
binrev.com
hackbloc.org
hellboundhackers.org
thesprawl.org
school-survival.net
www.totse.com
www.hackers.com
www.hack3r.com
www.phonelosers.net
www.nettwerked.net
www.undergroundnews.com
and to get familiar with telnet try reading some good articles on it and maybe signing on to some boards