To use function of cACL you must logged in as Super Administrator:

Login your Backend site:

Navigate to the cACL. Once you have logged in, hover over the Components link on the top taskbar, scroll down to cACL:

When you have selected the cACL, you will be sent to the cACL main page that lists all Administrators.

Select an Administrator to restric his right (e.g. giangnt )

When you have selected the Administrator (giangnt), you will be sent to the cACL Control Access Level of this Administrator (giangnt):

Look at Modules  box.

There are 3 options (Allow; Hide, Restrict). Default is allowed for all.

For this example, you allowed giangnt to manage Admin Modules only.

After that, you could choose Save task to save and back the previous page and set up other administrator or choose Apply task to Save and continue setting other or Cancel task to cancel limitation 

The Result.

Now access joomla backend with account giangnt to see the result:

The following screenshots shows you the end result of selecting limitative Components to administrator - giangnt . There are some differences between before limiting and after limiting: 

By default: giangnt could manage both Site Module and Admin Module  on the system

After limiting: giangnt could manage only Admin Module only.