the default telnet port is 23 (for telnet)

telnet drill.hackerslab.org

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