In Windows, the commands that are part of the command interpreter (cmd.exe), such as the dir, copy, ren, and such commands will display some help information with the /? switch.
Some examples:
dir /?
rename /?
copy /?
This is a hold out from the DOS days when many of the commands and programs used the backslash for the switches, and ? was used for displaying usage and help information, hence the /? switch.
Also, typing help at the command interpreter will also display a listing of all the command interpreter's commands. help <command_name> will also bring up help information as well.
Microsoft provides a Command Reference which has usage and options available for each command.