It has many components such as Extension Manager, Module Manager, Plug-in Manager, Template Manager and Language Manager.

Extension Manager:

Extensions are add-ons that expand the functionality of Joomla. Extensions are used to add capabilities to Joomla that do not exist in the standard package. Hundreds of Extensions are available for Joomla, with more being developed all of the time.

To extend the functionality of joomla, first of all login in Joomla Administrator Panel and go to Extensions -> Extension Manager.

There are mainly five things which performed extensibility of joomla, components are: Install, Update, Manage, Discover and Warnings.

Install: its enables the screen to install the extensibility functionality of joomla.

Update: Update screen provides the functionality to update the existence extension (i.e Joomla API, Joomla Extension etc.)

Manage: This screen will display the functionality to manage the joomla extensions via clicking Enable and Disable button.

Discover: This screen allows you to discover extensions that have not gone through the normal installation process.

Warning: This screen will display any warnings related to extensions you have installed in your Joomla installation.

Module Manager:

The Module Manager will display the screen where you could add and edit Joomla Modules such as Menu Module, Banner Module, Login Module and Breadcrumbs etc. In Joomla, Modules are used to display content and/or media around the main content.

To open the module manager, first of all login in Joomla Administrator Panel and go to Extensions -> Module Manager.

Module Manager contains mainly two things first one is Columns Header and Toolbar. Let’s take a look on these two.

Columns Header: Columns header contains the details of modules such as title, status, position etc. Let’s take a look on these in details.

Title: Title will display the module title.

Status: It will display whether module is activated/ deactivated or Enabled/Disabled.

Positions:  Position will display where or which position modules has been tagged in the website.

Ordering: it displays the modules order within a Position.

Type:  It displays the name of module. Joomla installs 20 standard Modules. Many Joomla! Extensions contribute additional Modules.

Pages: It shows whether module show in all page or any specific page.

Access: It displays the access type of modules.

Language: It displays the language of module.

Id: it shows the module id.

Toolbar: Toolbar having a collection of buttons which performs some specific task related to module manager.

Let’s take look in brief on these buttons.

New: This button is used to create new module.

Edit: It is used to edit the functionality of existence module.

Duplicate: It is used to create duplicate module of existence or selected module.

Publish: It is used to publish existence or selected module in your website.

Unpublish: it’s used to unpublish the selected module from website.

Trash: Moved selected modules to trash.

Options: This screen will display the module manager setting where you could change the default settings.

Help: This screen will display help screen of module manager.

Example: This is main page which having modules.

To create Module goes to Extensions -> Module Manager -> New. And fill all the information in text fields and click on ‘Save & Close’ button.

Now in the same manner you could create banner module, login module etc and it will display in your website.

Plug-in Manager:

The Plug-in Manager allows you to enable and disable Joomla plug-ins and to edit a plug-ins details and options. It is also useful for quickly enabling/disabling multiple plug-INS at once.

This screen will display you where you could enable or disable plugin, edit functionality of existence or selected plugin.

Here you can upload your custom plugin to perform some specific functionality in joomla..

Template Manager:

The Template Manager Styles screen is new to Joomla 1.6. It allows you to manage template styles which you can then apply to your Joomla installation. You can specify the default style to be applied to web pages in the public and administrator interfaces. You can also configure different styles for the various menu item web pages on your site.

 Styles allow to you have multiple different configurations of a template saved and then apply them on a whole website or accordingly website per pages.

To open template manager, first of all login in Joomla Administrator Panel and go to Extensions -> Template Manager.

In the template manager sections there are mainly two things: Style and Template. Style is used to manage the template styles where as template enables that how your website looks in web browser.

There are some buttons in toolbar which is at top right corner in joomla administrator panel.

Make Default: It is used to set selected template as default template of website.

Edit: Edit some template information such as logo, site description, site name, menu items, template color etc.

Duplicate: Create duplicate template styles of selected template style.

Delete: Delete selected template style.

Options: This screen will display template manager setting where you could change default settings of template such as permission and templates.

Help: It will display the help screen.

Language Manager:

In the Language Manager, Content Languages tab you can set Title, Native Title, Language Code, URL Language Code, Image Prefix, Status,  ordering and home of the installed languages.

To open the language manager in joomla, first of all login in Joomla Administrator Panel and go to Extensions -> Language Manager.

Now select Content tab from this section.

In this section, you can perform many task related to Content Language Manager such as create, edit, delete, publish, Unpublish etc with the help of buttons which is at top right corner of administrator panel.

So this is the complete description of Extensions Manager. I hope it might be useful for you.