When added to a course this enrolment plugin can enrol users onto a course automatically, either as they log in to your Moodle site or as they access to the course.
It was at first intended for use on site-wide courses such as "Moodle Help" or "Learner Voice".
In addition the plugin has advanced functionality to support automatically grouping and filtering users based upon their profile fields. Depending on how your user accounts are setup this may help you to give access to certain user groups.
Configuration of the plugin is managed by two capabilities which allow administrators to easily control who has access to the plugin.
New advanced user filtering (available from 2.3)
A complete rewrite of Autoenrol filter that use moodle standard availability interface adds great flexibility in user filtering.
The moodle profile availability core plugin unfortunately does not include language and authentication method.
If you need them, you can install additional availability plugins like Restriction by language and Restriction by authentication.
Warning for 2.3 and 2.3.1 users:
Release 2.3 add a new option to enable/disable new enrolments but not define "enabled" as default value for existing instances.
After upgrade all existing autoenrol instances do not permit new enrolments.
Please update to 2.3.2 in order to fix it. It enables new enrolments for all instances modified before 2.3 upgrade.