the default telnet port is 23 (for telnet)
telnet drill.hackerslab.org 23
they both have the same effect.
if you wanted to telnet to a webserver... say google...
telnet google.com 80
check out a tutorial or two...
www.google.com and search for telnet tutorials
http://www.chem.ox.ac.uk/it/telnet.html looks good