This gives information about people based on their login names. It can also, given a real name, look up all login names with that in the real name.
Finger alone gives a list of who is on with login name, real name, and where from.
Finger name gives information based on name . You can look up information on a person, sort of like with finger, with it. This is a quick way to get help on command options. Man -k searches by keyword instead of by command. This gives information about sites based on their name or IP address.