@SYNTAX:who@

Without parameters, shows all users and their user infos
on the current channel. If you specify a channel, shows
the all users of the given channel.

If you specify an string with wildcards, you will be
shown all users whose nick, userhost or realname matches
the wildcard expression.

If a channel is secret or private and you're not on it,
you will be shown only those channel members, who do not 
have the invisible (+i) mode set.

Examples:
   /WHO          - Shows users on current channel
   /WHO #irssi   - Shows users on channel #irssi
   /WHO timo*    - Shows users whose nick, userhost,
                   or realname begins with string 'timo'

See also: WHOIS, CHANNEL