Despite claims to the contrary Joomla 1.5 does have an ACL system. It is simple so that it can be easily understood and quickly utilized but when if is fully understood can be very useful.

To help you we have created a simple table with an overview of who can do what.

Joomla ACL explained

Front-end Groups Back-end Groups
Guest Registered Author Editor Publisher Manager Admin Super-Admin
View "public" content Yes Yes Yes Yes Yes Yes Yes Yes
View "registered" content - Yes Yes Yes Yes Yes Yes Yes
View "special" content - - Yes Yes Yes Yes Yes Yes
Create new content - - Yes Yes Yes Yes Yes Yes
Edit own content - - Yes Yes Yes Yes Yes Yes
Edit all content - - - Yes Yes Yes Yes Yes
Publish new content - - - - Yes Yes Yes Yes
Access the Administrator page - - - - - Yes Yes Yes
Create new users - - - - - - Yes Yes
Install extensions - - - - - - Yes Yes
Change the template - - - - - - - Yes
Change site settings - - - - - - - Yes