The Online Users module is used to display a list of users that are either on the site or on that particular page. It is in the module category Statistics.
The Online Users module has three different options:
Display Avatars?
This decides whether the users avatar is displayed in the list (Yes) or whether the username is displayed in the list (No).
Max online users to show
This is the maximum number of users that should be listed in the list. If there are more users, then they will just not be shown.
Show Users For This Page Only?
You may set this to only show the users viewing this page (Yes) or to show all the users on the site (No).