Can someone please explain the rights given to users that are assigned any of the following access levels shown in the image.
There are a few parts to this.
The group and the viewing access level. A person is part of a group. E.g Administrator.
A group is assigned a viewing access level. A group can have multiple viewing access levels. A viewing access level can have the same name as a group.
If someone has a viewing access level they can view that particular content, component, module etc.
To further complicate things there is viewing access and edit access.
For example you could set a module to be editable only by Administrators but viewable by Registered users.
The same is true for categories, articles, components, and plugins (usually there is edit access only for plugins).
As an example a teacher may wish to be able to view teachers articles and students articles. So you may have two viewing access levels: student and teacher. And two groups, student and teacher. But the teacher group may have access to both student and teacher viewing access levels. But you may wish for teachers to be able to view but not edit students articles.
And for students they should view students articles but not view or edit teachers articles. This is entirely possible with Joomla! out of the box.
Much more detailed information can be found here: https://docs.joomla.org/J2.5:Access_Control_List_Tutorial
Although it is Joomla! 2.5.x it is still applicable for Joomla! 3.x
Please check the full explanation in the following link:
- User Group Access levels explained in simple terms https://docs.joomla.org/User_Group_Access_levels_explained_in_simple_terms
please visit Access Control List Tutorial for access level explanations with examples. https://docs.joomla.org/J3.x:Access_Control_List_Tutorial